• HMRC considers that any informal payment requests have been ignored and formal recovery action is warranted.

The date of issue is important, because it starts the clock for key deadlines (see next section).

Time-limits for challenging tax determinations

One of the major issues with tax determinations is understanding when you can displace them by filing the missing return.

• If the outstanding return is submitted within 12 months of the date of the determination, it will supersede the determination.

• If not within 12 months, then the return must still be submitted within 3 years of the power to make the determination first becoming exercisable.

If neither deadline is met, the tax determination stands and cannot be displaced by the return.

Because these rules apply in the 2025/26 tax year they are unchanged but remain critical.

Interest, surcharges and enforcement following a tax determination

Once a tax determination is in place:

• HMRC can pursue recovery of the tax as if the return indicated that amount due.

• Interest and surcharges may begin to accrue from dates relevant to the original filing obligations.

• The taxpayer may lose the right to appeal against the determination per se; the effect is that the only way to challenge the amount is by filing the proper return and satisfying the displacement rules.

Special relief in relation to tax determinations

There is a concept of “special overpayment relief” which can apply in cases where a tax determination has resulted in an excessive liability. In essence, if it would be unconscionable for HMRC to demand recovery, a claim may be available.

The conditions include:

• The tax determination is manifestly excessive;

• The taxpayer’s affairs are otherwise up to date or arrangements have been made;

• The person has not already claimed relief (or there are exceptional further circumstances).

Importantly, there is no statutory time limit for these claims, although HMRC’s acceptance is discretionary.

For 2025/26 this remains valid — so if you believe a tax determination is unfair you should consider whether special relief is relevant.

Updated 2025/26 considerations for tax determinations

For the 2025/26 tax year, the broad rules around tax determinations remain as previously outlined. Key points to note:

• HMRC issued guidance in April 2025 regarding supersession of determinations under the Finance (No. 2) Act 2023. That guidance confirms the 12-month and 3-year deadlines still apply.

• The general three-year window for issuing a determination remains (for self-assessment cases) unless there is some extended assessment reason.

• Filing obligations and digital deadlines continue to be important; non-filing remains a trigger for HMRC to consider issuing a determination.

• Given the increasing use of data-matching and risk-based compliance by HMRC, the risk of a tax determination being issued for non-filing is higher than ever.

So for 2025/26, if you have not filed a return for a year in which you should have done so, you must assume the possibility of a tax determination and act promptly to file the return or make contact with HMRC.

How Trueman Brown can help you manage tax determinations

If you have received a notification of a tax determination, are at risk of one, or simply want to avoid the scenario in the first place, our team at Trueman Brown is ready to assist. We can help you by:

• Reviewing your outstanding filing obligations and identifying whether a tax determination could be issued;

• Analysing the amount estimated by HMRC (if issued) and comparing it to what the correct return would show;

• Advising whether the return may still be filed in time to displace the determination;

• Guiding you through any claim for special relief if the determination appears excessive;

• Liaising with HMRC on your behalf to negotiate payment, agree instalments or avoid enforcement action.

If you’d like to discuss tax determinations for the 2025/26 tax year or earlier years, please contact us:

Email: mark@truemanbrown.co.uk
Phone: 01708 397262

We look forward to helping you take control of the situation and minimise risk.

FAQ

Q 1: What is a tax determination?
A: It is a formal calculation by HMRC of the tax you owe when you have failed to submit a return.

Q 2: Can I appeal against a tax determination?
A: You cannot appeal the determination per se; you may instead file the missing return within the deadlines to displace it, or claim special relief if appropriate.

Q 3: What are the deadlines for filing after a tax determination?
A: The missing return must be filed within either 12 months of the determination date or three years from when the power to make it first became exercisable – whichever applies.

Q 4: Will interest and penalties apply to a tax determination?
A: Yes — once the determination stands, HMRC can add interest and surcharges and start enforcement action as if you had submitted a return showing the same tax.

Q 5: What is “special relief” in relation to tax determinations?
A: If it would be “unconscionable” for HMRC to enforce the determination — for example because of illness, failure to receive notices or insolvency — you could claim special relief. There is no fixed time-limit for doing so.

Q 6: What should I do now if I haven’t filed a return for 2023/24 or an earlier year?
A: You should file the required return as soon as possible, check whether a tax determination may already have been or might be issued, and engage professional advice to identify if you can still displace a determination or need to claim special relief.

If you’d like personalised advice on managing tax determinations for your unique circumstances, please get in touch with us at Trueman Brown via mark@truemanbrown.co.uk or 01708 397262.