In Tinkler v HMRC [2021] UKSC 39, the Supreme Court examined the conditions for estoppel by convention, finding that an agents action in complying with an enquiry notice rendered a tax enquiry and a subsequent issued closure notices valid, even though the original enquiry notice was invalid. 

  • On 11 January 2005, Mr Tinkler engaged a new tax agent.
  • Shortly afterwards HMRC were given a new address for Mr Tinkler which they processed and used.
  • HMRC changed Mr Tinkler’s address back to his old address. This was made without notification or discussions with Mr Tinkler or his agent.
  • HMRC opened an enquiry into the tax 2003/04 tax return sending the enquiry notice to the old address and a copy to his agent.
  • The agent acknowledged receipt and claimed an Income Tax loss that had been omitted from his return conceding the amendment could not be immediately processed due to the ongoing enquiry.
  • The agent engaged with the enquiry process with HMRC and Closure notices were issued on 30 August 2012.

Mr Tinkler Appealed on the preliminary issue of whether the enquiry had been validly opened, if not, the closure notices would also be invalid. The two primary issues in the case were:

  • Had the enquiry notice been issued validly.
  • If not, did estoppel by convention apply, did the actions of the parties (HMRC and the taxpayer through their agent) in progressing the enquiry render the enquiry validly opened as they had both made and acknowledged the mistaken assumption that it had been validly opened.

The First Tier Tribunal found:

  • The accountants did not have the authority to receive enquiry notices on behalf of Mr Tinkler.
  • However, the notice of enquiry was validly served on the taxpayer (despite being sent to the wrong address) as his agent had made him aware of it prior to the closure of the enquiry window.
  • Estoppel by convention applied as the agent, acting on the taxpayer's authority, had complied with the enquiry notice and that compliance rendered it too late to review the underlying validity of the notice.

Mr Tinkler appealed (and HMRC cross-appealed) to the Upper Tribunal (UT) who found:

  • A notice of enquiry could be validly served on a taxpayer via his agent and the notice in question was therefore valid.
  • An enquiry notice does not become valid because the intended recipient finds out about it from a different source. The incorrect address would have rendered the enquiry notice invalid if it had not been validly served on the agent.
  • Academically, as the enquiry had been validly opened, estoppel by convention could not apply as it would undermine the legislative requirement that the taxpayer needed to be notified of the enquiry.

Mr Tinkler appealed to the Court of Appeal (CoA) who reversed the UT decision finding that:

  • The accountant’s authority to interact with HMRC was limited in certain circumstances, which included the issuing of enquiry notices.
  • Enquiry notices had to be issued to the taxpayer thus the enquiry had not been validly opened as they were issued to the wrong address.
  • Estoppel by convention did not prevent the challenge to the enquiry notice as:
    • The accountant’s actions in complying with the enquiry notice were on the assumption that HMRC had opened a valid enquiry.
    • This was not the case and it was this misrepresentation by HMRC that had caused the accountants’ compliance.

HMRC appealed to the SC on the estoppel by convention issue who found:

  • No formal contract or transaction between the parties (the taxpayer and HMRC) was required on which to ‘hang’ an estoppel by convention, it could be considered.
  • HMRC satisfied all the requirements for establishing an estoppel by convention as:
    • Both parties shared a ‘common assumption’,  that an enquiry had been validly opened.
    • The accountant’s actions in replying and engaging with the enquiry process confirmed it was sharing and acting on that common assumption.
    • HMRC relied on the accountant’s affirmation of that common assumption in its dealings in progressing the enquiry.
    • HMRC’s reliance on the common assumption was detrimental as they could have sent an alternative, and valid, enquiry notice prior to the enquiry window shutting.
    • If there were objections to the enquiry notice at the time, it would have allowed HMRC to issue a correct notice, and it was unconscionable to raise the point over nine years later.
  • The statutory provisions required the taxpayer to be notified of the enquiry, the taxpayer had been so notified and estoppel by convention would not, therefore, conflict with the legislation.


This case highlights the importance of checking enquiry notices for their validity before engaging with HMRC. The actions of the taxpayer and their agent rendered what would otherwise have been an invalid enquiry valid.

Pulling such an argument out of the hat at a later date is unlikely to have any merit, as Lord Burrows stated in the case: "Mr Tinkler and his advisors had looked at the case at a late stage and taken a technical point, that the notice of enquiry was sent to the wrong address, even though that has not caused any prejudice."

Useful guides on this topic

Closure notices
When does HMRC issue a Closure Notice? Can a taxpayer demand one? Are there appeal rights?

How to appeal an HMRC decision
Disagree with a HMRC decision? How to appeal, what type of decision can you appeal and what are your different options when you disagree with HMRC? What are the key steps in making an appeal?

Closure notice invalid: notice of enquiry not validly served (Court of Appeal decision)
In William Tinkler v HMRC [2019] EWCA 1392 the Court of Appeal ruled that a notice of an enquiry sent to a tax agent was not validly served on a taxpayer; the subsequent closure notice was also invalid.

Notice of enquiry can be validly served via an agent (Upper Tribunal decision)
In William Tinkler v HMRC [2018] UKUT 0073 the Upper Tribunal (UT) decided that a copy of notice of an enquiry under section 9A TMA 1970 sent to a tax agent was validly served on a taxpayer.

External links

Tinkler v HMRC [2021] UKSC 39 

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