Cases

Tinkler v HMRC: When A Defective Notice Still Binds You

HMRC sent Mr Tinkler's enquiry notice to the wrong address in 2005. Nine years later, the Supreme Court still held him to it. Here is what that means for any appellant facing a procedurally defective HMRC notice.

Liam Williams

Liam Williams

— 16 min read
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Your HMRC notice has a defect on its face—wrong address, wrong year, wrong officer name. Does that kill HMRC's enquiry? After Tinkler, the answer is: only if you raise the point quickly, and only if your conduct does not betray you.

Tinkler v HMRC [2021] UKSC 39 is the Supreme Court's leading authority on what happens when a procedural defect in an HMRC notice meets years of correspondence pretending it does not exist. HMRC posted Mr Tinkler's section 9A enquiry notice to a house he had moved out of nine months earlier. His accountants got a copy, accepted the enquiry as valid, and corresponded with HMRC for seven years. Only after the closure notice arrived—nearly a decade after the original error—did his team spot the defect. The Supreme Court, unanimously, said no.

The case has nothing to do with discovery assessments on its facts: the defective document was a section 9A enquiry notice, and the closure notice under section 28A crystallised the dispute. But the doctrine the Court reaffirmed—estoppel by convention—is now routinely deployed by HMRC to defeat late procedural challenges to discovery assessments and other notices. Tinkler is the procedural-validity authority every unrepresented appellant should understand before deciding whether to raise—or how to preserve—a defect point.

What Tinkler Actually Decided

Mr William Andrew Tinkler, founder of the Stobart Group, filed his 2003-04 self-assessment return on 24 February 2005 and paid the tax shown as due (£701,990.96). In a letter dated 6 July 2005, his accountants BDO Stoy Hayward wrote to HMRC asserting that a gilt-strip loss of approximately £2.5 million had been wrongly omitted, which—if valid—would have generated a repayment of more than £600,000 of income tax.

The Defective Notice

Mr Tinkler had moved out of his Heybridge Lane address in October 2004 and settled at Station Road. The return he filed in February 2005 gave Station Road, and by mid-March HMRC had written to him there acknowledging his tax payment.

Then, on 1 July 2005, an HMRC officer (Mr Mackay) issued a section 9A notice addressed to Mr Tinkler at the old Heybridge Lane address. The notice was delivered there and never forwarded. Mr Mackay sent a covering letter to BDO at BDO's own address, enclosing a copy and saying the notice "has today been issued to your client".

That was the defect. Under section 115 TMA 1970, HMRC may serve documents by post "at his usual or last known place of residence". Heybridge Lane was neither.

Nine Years Of Silence

BDO's letter of 6 July 2005 affirmatively endorsed the enquiry: BDO could not amend the return, the letter said, because "the Return is now the subject of a section 9A TMA 1970 enquiry". Through August, October and November 2005, BDO answered HMRC's substantive questions about Mr Tinkler's Ukrainian property transactions. The FTT later inferred that Mr Tinkler—or at least his personal assistant—was told about the enquiry in November 2005, still inside the twelve-month window during which HMRC could have re-served.

Nobody told HMRC about the address mistake. On 30 August 2012—more than seven years later—HMRC issued a closure notice under section 28A TMA, rejecting the gilt-strip loss and confirming the original tax of £701,990.96 as correct. It was only in late 2015, two months before the FTT hearing, that Mr Tinkler's team amended the notice of appeal to argue that the section 9A notice had never been validly served. By then, ten years had passed.

The Question The Supreme Court Answered

The procedural journey ran the full appellate gauntlet. The First-tier Tribunal (Judge Mosedale) and Upper Tribunal (Judges Berner and Sinfield) both dismissed the validity challenge. The Court of Appeal (Hamblen LJ leading) restored Mr Tinkler's win: BDO had no authority to receive a formal enquiry notice, and estoppel by convention could not save HMRC because BDO had never "assumed responsibility" for the assumption that an enquiry had been opened.

The Supreme Court, on 30 July 2021, sided with HMRC unanimously. Lord Burrows gave the leading judgment (with Lord Hodge, Lord Briggs, Lady Arden and Lady Rose). The question was narrow: did estoppel by convention prevent Mr Tinkler from denying that a valid enquiry had been opened, given the way BDO had behaved? It did. And in answering that question, the Court restated the modern test for estoppel by convention in terms that now govern every HMRC notice-validity dispute below the Supreme Court.

Why Tinkler Matters Beyond Its Own Facts

Tinkler is not, on its facts, a discovery-assessment case. The defective document was a section 9A enquiry notice. But the case-law downstream of Tinkler has applied the estoppel-by-convention framework to discovery-assessment validity challenges, treating the procedural defect in a section 29 assessment in the same way as the defect in Tinkler's section 9A notice. The leading downstream decision is Rakshit & Ors v HMRC (FTT 2023); its Upper Tribunal sequel, Scatola (2025), dismissed the appellants' procedural challenges and allowed HMRC's cross-appeal on discovery-assessment validity (the estoppel point not having been pursued on appeal). See the post-Tinkler section below.

The doctrine reaches further still. Recent FTT decisions have applied it to customs C18 demand notices (MWL International, Quantum House), VAT assessments (Queenscourt), and a gilt-strip closure notice with strikingly similar facts to Tinkler itself (Cattrell).

If HMRC has issued any notice that might be procedurally defective—a Schedule 36 information notice, a closure notice, a discovery assessment, a penalty assessment, a customs demand—and you or your adviser has corresponded with HMRC on the footing that the notice is valid, Tinkler is on the table.

The Estoppel-By-Convention Test

Estoppel by convention is, in Lord Burrows's own words, "notoriously difficult to pin down" (UKSC para 1). The doctrine prevents a party from going back on a state of facts or law that the parties have shared and acted on, where it would be unjust to allow them to do so. It is not estoppel by representation (which requires a clear statement of fact) or promissory estoppel (which requires a promise)—it is grafted onto the way the parties have actually conducted themselves.

The modern test comes from HMRC v Benchdollar Ltd [2009] EWHC 1310 (Ch), where Briggs J (later Lord Briggs of the Supreme Court) set out five principles, amended in Blindley Heath Investments Ltd v Bass [2015] EWCA Civ 1023 to add a "crossing the line" element to the first principle. Tinkler confirms that test as the law (UKSC para 78).

The Five Principles, Amended

As Lord Burrows set them out (UKSC paras 45 and 50):

  1. A shared common assumption that has "crossed the line". Both parties privately understanding the position the same way is not enough—the assumption must have been manifested in a statement or conduct between them.
  2. Assumption of responsibility. The party against whom the estoppel is invoked must have communicated something that conveys to the other party an expectation of reliance.
  3. Reliance in fact. The party invoking the estoppel must actually have relied on the shared assumption, not on its own independent view.
  4. Subsequent mutual dealings. The reliance must have happened in the context of some subsequent dealing between the parties.
  5. Detriment, or benefit conferred. Something must have happened that makes it "unjust or unconscionable" to go back on the shared position.

The "crossing the line" requirement is the doctrine's filter against silent assumptions. In Lord Burrows's language at paragraph 34, "there must be a statement or conduct ... between the parties that 'crosses the line'". An unspoken thought is not enough. In Tinkler, BDO's 6 July 2005 letter expressly acknowledged that the return was now under enquiry; that crossed the line.

Read in isolation the principles sound demanding, but in practice they are easier for HMRC to satisfy than they look. Everyday compliance correspondence often does cross the line: a reply that says "we will respond to your enquiry on the following points" or "in response to your section 9A notice of [date]" is, on HMRC's submission, a statement that both crosses the line and assumes responsibility.

How The Five Principles Applied To Mr Tinkler

Lord Burrows worked through each principle in turn and found each satisfied (UKSC paras 51-66).

Principles (i), (ii) And (iv): Crossing The Line And Sustained Dealings

Both BDO and HMRC had communicated with each other on the basis that an enquiry had been validly opened. BDO's 6 July 2005 letter explicitly stated that "the Return is now the subject of a section 9A TMA 1970 enquiry". The line was crossed (paras 55-56).

On responsibility, the Court of Appeal had held that BDO never "assumed responsibility" for the assumption because HMRC had induced it. Lord Burrows disagreed (paras 57-61). BDO did not merely accept HMRC's word: it affirmatively endorsed the enquiry's existence in writing and then dealt with HMRC on that footing through reminders, telephone calls and substantive responses for years. That was enough to convey to HMRC an understanding that BDO expected HMRC to rely on the assumption. The fact that HMRC had originally introduced the mistake did not defeat the finding—a party can rely on an estoppel by convention even where it created the mistake itself (Amalgamated Investment & Property Co Ltd v Texas Commerce International Bank Ltd [1982] QB 84).

Mr Tinkler's counsel argued that "mutual dealings" should be narrowly construed to require something like a contractual transaction. Lord Burrows rejected that (paras 70-77). The years of correspondence about the Ukrainian property questions, the repayment cheque, the gilt-strip loss and the closure-notice process were plainly enough.

Principles (iii) And (v): Reliance And "Particularly Unconscionable" Detriment

HMRC's reliance on the shared assumption took the form of not checking whether the notice had reached Mr Tinkler before the twelve-month enquiry window closed in January 2006. Lord Burrows's analysis at paragraph 61 treats that as reliance enough; Lord Briggs in his concurrence at paragraph 91 puts the same point in shorter form—HMRC relied on BDO's subscription to the common assumption "even if only in the negative sense that the Revenue would not thereafter check that the enquiry had been duly opened, and notice of it duly served on Mr Tinkler, before the limitation period for doing so ran out". A taxpayer hoping to defeat Tinkler on the reliance limb is unlikely to succeed by arguing HMRC was not actively misled—the doctrine treats HMRC's failure to take protective steps as reliance enough.

On detriment, the enquiry window closed in January 2006 without re-service, and the substantive enquiry result was then crystallised in the 2012 closure notice. By the time Mr Tinkler took the validity point, more than nine years had passed. At paragraph 65, Lord Burrows wrote:

"[I]t may be thought particularly unconscionable for him to raise this point for the first time over nine years later."

That phrasing—"particularly unconscionable"—is the doctrine's centre of gravity. It tells a taxpayer that the longer the delay, the harder Tinkler hits. The Supreme Court was also influenced by the FTT finding that Mr Tinkler or his personal assistant had known about the enquiry in November 2005, while there was still time for HMRC to re-serve. Had they told HMRC then, the dispute would never have arisen.

What This Means If You Have Received A Defective Notice

The practical position splits along three lines. First, a word on what "defective" means in this context.

What A Defective Notice Looks Like

Pull out the HMRC letter and check five things:

  • The address. Compare the delivery address on the envelope and the salutation block with the address on your most recent return and any correspondence in the preceding 12 months. A notice sent to your previous home or a closed business address—when HMRC had your current address on file—is Tinkler-style defective.
  • The tax year or period. A notice that names the wrong year of assessment (for example "2020-21" when the dispute is about 2021-22) is harder to cure than an address mistake; section 114 TMA usually cannot save it.
  • The taxpayer name. A wholly wrong name is a defect; a misspelt forename or missing middle initial is the sort of "want of form" that section 114 TMA was designed to cure.
  • The officer's authority. Section 9A notices must be issued by "an officer of the Board". A signature block with no named officer, or a notice issued by a junior caseworker without HMRC's delegated authority, can be challenged—though Tinkler's estoppel logic still applies.
  • The deemed-receipt date. Under section 7 of the Interpretation Act 1978, first-class post is deemed received two working days after posting; second-class four. If HMRC posted close to the 12-month enquiry deadline, the deemed-receipt date may push service outside the window.

A typo or wrong amount is not, on its own, fatal—section 114 cures most "want of form" defects. The defects Tinkler genuinely engages are those that go to whether the notice ever properly reached the taxpayer in the period the statute allowed.

If The Notice Has Just Arrived

The most important rule when you spot a defect is: raise the validity point in the first response, and do not affirm the notice's validity in the meantime. A response that says "we will provide the information requested in your enquiry letter of [date]" is, on the Tinkler analysis, a statement that crosses the line. Better wording opens with a without-prejudice reservation (see below).

If a closure notice or assessment has been issued, use the 30 days window under section 31A TMA 1970 to lodge a protective notice of appeal. The notice of appeal must specify the grounds (section 31A(5)); list "validity of the enquiry/assessment" as one of them.

If An Agent Has Been Responding On Your Behalf

This is Tinkler itself. If you are reading this with a closure notice in front of you and an agent who has been corresponding for years, the fear you are feeling is rational—the door may already be closing. But Rakshit and Cattrell both show that the door is not closed where the agent never actually accepted the notice's validity. The forensic question is precise: pull every letter your agent sent HMRC and search for the first one that uses the word "enquiry" or "assessment" in a way that treats it as live. That letter is the start of your problem; everything before it is your defence.

The legal question is fact-sensitive. Did the agent affirmatively endorse the notice's validity, or simply respond to HMRC's substantive questions? Did the agent ever push back? If the correspondence consistently treated the enquiry as live and properly opened—especially in writing—you are in Tinkler territory. If the agent never expressly accepted validity, you are closer to Rakshit or Cattrell.

If You Are Already At Closure Notice Or Assessment Stage

If a closure notice or assessment has been issued and the defect went unnoticed all the way through, the path forward is narrow but not closed:

  1. Move quickly. Every additional month of delay strengthens HMRC's "particularly unconscionable" argument.
  2. Document the absence of endorsement. Comb your correspondence for moments where validity was not expressly accepted; the Rakshit-style defence depends on showing the line was never crossed.
  3. Lodge the appeal within 30 days of the closure notice or assessment. Missing that deadline pushes you onto the late-appeal path, which engages the Martland three-stage test—and Katib v HMRC attributes adviser failings to the taxpayer.
  4. Consider whether the substantive merits stand independently. Even if Tinkler defeats the procedural challenge, the underlying assessment may be vulnerable on its own terms.

If You Win On Tinkler, What Happens Next?

Winning a Tinkler validity point does not always end the dispute—but it changes what HMRC can do:

  • If the 12-month enquiry window is still open, HMRC can re-serve a fresh section 9A notice at the correct address. Tinkler relief is procedural-only.
  • If the enquiry window has closed, HMRC's only route is a section 29 discovery assessment—which has higher gateway requirements (carelessness, deliberate behaviour, or the hypothetical-officer test from Charlton and HMRC v Tooth).
  • If the relevant discovery time limit (4, 6, or 20 years depending on behaviour) has also passed, HMRC is usually out of routes for the year in question.

A Tinkler win is most valuable where time has put HMRC's substantive routes out of reach. Where the windows remain open, the practical value is delay and forced restart—not extinction of the underlying claim.

A Worked Example

You moved from Manchester to Bristol in spring 2024, updating your address on your 2023-24 self-assessment return filed that October. In November 2024 HMRC issued a section 9A enquiry notice—but the computer system picked up your old Manchester address, and the new occupier binned the envelope. Your accountant (copied in) replied in December 2024: "Thank you for your letter of [date]. We will respond on the points raised within thirty days." Through 2025 the accountant answered HMRC's substantive questions. In March 2026 HMRC issued a closure notice making a £40,000 amendment, and your accountant lodged a protective appeal. Only then does a new adviser notice the address defect.

Tinkler applies cleanly. The December 2024 reply crosses the line (i) and arguably assumes responsibility (ii); HMRC's failure to verify service is reliance (iii); a year of correspondence is mutual dealing (iv); and the closure-notice window has now expired, locking in detriment (v). Your best arguments are that the accountant's opening reply was procedural courtesy rather than affirmative endorsement, and that an eighteen-month delay falls well short of Tinkler's nine years on the "particularly unconscionable" limb. Neither argument is guaranteed; both turn on the exact wording of every reply. The Supreme Court found in HMRC's favour on facts very similar to many ordinary enquiries.

How To Preserve A Validity Challenge In Your Replies

If you want to keep the validity point alive, your replies have to be drafted with that in mind.

Without-Prejudice Wording

A standard opener for any reply to a defective notice is:

"Without prejudice to whether HMRC has validly served a notice / opened an enquiry / made an assessment, and expressly reserving the right to challenge validity in any subsequent appeal, we respond as follows ..."

This wording will not by itself defeat the Tinkler analysis—the Supreme Court was clear that conduct as much as words can cross the line. But it does prevent your reply being read as an affirmative endorsement, and gives a clean line for cross-examination if it comes to it.

Protective Appeal Under Section 31A

The most reliable preservation move is to file a section 31A notice of appeal within 30 days of any appealable HMRC decision, expressly listing validity as a ground. The statutory review route (with a 45 days review period) and the tribunal route both preserve the validity argument so long as it is in the notice.

When To Engage A Tax Adviser

If the notice has a defect, you have responded on the substance, and you are unsure whether your conduct has crossed the line, this is the point at which a tax adviser becomes high-value. The strategic question—raise validity now, hold it, or abandon it and focus on the merits—is fact-sensitive in a way that is hard to do unaided. Tinkler costs taxpayers money when raised badly; it can equally rescue them when raised well. The line between the two is usually drafting.

If you cannot afford a paid adviser, the following charities help unrepresented appellants free of charge: TaxAid (for working-age people on lower incomes), Tax Help for Older People (for pensioners on lower incomes), the Low Incomes Tax Reform Group (general guidance), and Citizens Advice (triage and signposting). HMRC's Extra Support Team provides additional help where ill-health, disability, or vulnerability is in play.

What Tinkler Cannot Save You From

The doctrine has limits. Six in particular matter for an unrepresented appellant:

  1. Section 114 will not cure a wrong-year notice. Section 114(2) protects notices against errors in the name of the person, the description of the property and the amount of tax. It does not save a notice that refers to the wrong tax year—the year of assessment is part of the "substance and effect" the notice must get right.

  2. Estoppel against the Crown is essentially one-way. HMRC can deploy Tinkler against taxpayers who have run with a defective notice, but taxpayers cannot generally use it to bind HMRC to concessions in correspondence or to officers' representations about the tax position. If you are tempted to construct a Tinkler-style estoppel against HMRC, take advice.

  3. The Katib rule attributes agent failings to you. If you missed the section 31A appeal window because your accountant did not raise the validity point, Katib v HMRC [2019] UKUT 189 (TCC)—endorsed by the Court of Appeal in Medpro—says the agent's failure is your failure for the purposes of late-appeal applications.

  4. The substantive merits are unaffected. Winning on procedural validity does not decide the underlying tax position; losing on procedural validity does not preclude attacking the assessment on its substantive limbs. If HMRC's notice fails, a different officer, a re-served notice (if time permits) or a discovery assessment may still be available to them.

  5. The section 31A deadline is unforgiving. If you do not appeal within 30 days of the appealable decision, the appeal is out of time. There is no "I was hoping to win on validity so I did not file" defence. File the protective appeal; argue the validity point inside it.

  6. New points at the Upper Tribunal need permission. A validity point that was never argued at the FTT is not an error of law in the FTT decision (see Edwards v Bairstow and our Upper Tribunal appeal guide). Permission to take a new point on appeal is granted only exceptionally.

How Tinkler Has Been Applied Since 2021

The post-Tinkler case-law splits cleanly. Where the taxpayer or agent affirmatively engaged with the notice on the footing that it was valid, Tinkler bites. Where the validity point was raised early and maintained, the line was not crossed and the estoppel framework gives the taxpayer a route through.

Taxpayer wins. In Rakshit & Ors v HMRC [2023] UKFTT 1044 (TC), three pairs of SDLT-scheme participants challenged section 75A FA 2003 discovery assessments; the FTT (Judge Aleksander) found they had contested validity throughout and HMRC failed on estoppel (though the taxpayers lost on the substantive validity arguments). Alastair Cattrell v HMRC [2024] UKFTT 67 (TC) involved the same gilt-strip product for the same 2003-04 tax year as Tinkler; the FTT held that the taxpayer's "representative sample agreement" with HMRC had not crossed the line.

Taxpayer losses. Queenscourt Ltd v HMRC [2024] UKFTT 460 (TC) applied Tinkler in a VAT context: the taxpayer had treated VAT assessments as valid through extended correspondence and was estopped from a late challenge. Quantum House Holdings Ltd v HMRC [2025] UKFTT 117 (TC) applied Tinkler to a customs C18 demand notice; HMRC succeeded after the taxpayer engaged with the demand on the merits without flagging validity.

Key Legislation And Resources

The Judgment

Legislation

Key Cases

HMRC Guidance

On This Site

Tinkler tells you what happens when an HMRC notice is procedurally defective; Tooth tells you what "deliberate" means in section 29(4); Wilkes tells you what "income" means in section 29(1)(a). Together they map the boundaries of HMRC's enquiry and discovery powers—and the conduct that locks taxpayers into accepting them.

This article is for informational purposes only and does not constitute legal or tax advice. For advice specific to your situation, consult a qualified tax adviser, accountant, or solicitor.

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