The uncertain tax treatment regime has spent four years as a large-business obligation that most advisers never touch. A consultation published on 12 March 2026 proposes to change that in four ways at once, and one of them reverses an assumption the profession has worked with for a generation.

Today, where HMRC has expressed no view on a genuinely arguable point, an adviser takes the better reading, documents it and files. Under the proposal, the absence of an HMRC view becomes the thing that creates the duty to notify.

This article sets out what the regime does now, what the consultation proposes, which parts are settled and which are open questions, and what advisers can sensibly do while the government response is awaited.

⚠️ Watch: This is a closed consultation awaiting a government response. Nothing here is law. The consultation ran from 12 March 2026 and closed on 4 June 2026, and a government response is awaited. Any legislation would follow in the next available Finance Bill.

The regime reaches large companies and partnerships only: turnover above £200m, or a balance sheet total above £2bn. Below those figures, it does not apply at all.

Three, at present: corporation tax, VAT, and income tax including amounts collected through PAYE.

A notification is required where a tax treatment meets one of two conditions and more than £5m of tax advantage rides on it:

• The accounting provision trigger. A provision has been recognised in the accounts to reflect the probability that a different tax treatment will be applied.
• The known position trigger. The treatment relies on an interpretation that is not in accordance with the way in which it is known that HMRC would interpret or apply the law.

The second is the important one for understanding the proposal. It bites where HMRC's position is known and the taxpayer departs from it. Silence from HMRC currently keeps a taxpayer outside the trigger.

Modest volumes. As at 1 January 2026, more than 30 notifications had been made since the regime began, covering an estimated £1bn of potential tax at risk.

The headline change. Any individual, and any trust, would fall within the regime wherever a qualifying uncertainty produces a tax advantage above £5m. No wealth test, no income test, no turnover test sits underneath that threshold.

For a substantial estate, a single significant disposal, or a one-off transaction, £5m of advantage is a lower bar than it first sounds. The regime stops being a large-corporate compliance exercise and becomes something a private client adviser may meet.

Stamp duty land tax, national insurance contributions, construction industry scheme withholding obligations, capital gains tax and inheritance tax would join corporation tax, VAT and income tax.

The addition of CGT and IHT is what pulls the regime into private client work, and it pairs naturally with the extension to individuals and trusts.

The third proposal introduces notification where there is more than one credible legal interpretation and HMRC's view is not known. It is aimed at uncertainties that currently escape both existing triggers, particularly around novel products or processes on which no HMRC guidance exists. Transfer pricing calculations would be carved out.

“Today HMRC's silence protects the filing position. Under this proposal, the silence is what creates the obligation.”

The practical consequence lands well before any dispute, and it lands on the adviser. Somebody has to identify the second interpretation, assess whether it is credible, and record the analysis. That is a documentation duty wearing the clothes of a notification duty.

The fourth proposal tightens the general exemption from notification. Today, no notification is needed where it is reasonable to conclude that HMRC already has the relevant information. Under the proposal, the exemption would apply only where the taxpayer holds confirmation from HMRC that it is aware of the uncertainty.

The shift moves the risk of HMRC's own silence onto the taxpayer: a slow or ambiguous response from HMRC would itself leave open whether notification is still required. For taxpayers without a customer compliance manager — which is most individuals and trusts — obtaining that confirmation is not a routine exercise.

A consultation is not a decision, and this one is explicit about which parts remain open. Reading it as settled policy would be a mistake.

The professional bodies did not wave the package through: the ATT recommended leaving IHT out of any extension, and ICAEW opposed the CIS, NICs and IHT additions while accepting CGT — a reminder that the government response may not carry every element forward.

📌 Key date: The consultation closed on 4 June 2026. What is new is the wave of professional analysis and the awaited government response, not the document itself. Legislation would come in the next available Finance Bill and apply to returns filed after 1 April the following year.

Filing a notification is a small task. Knowing that you need to file one is the hard part, and it requires somebody to have asked, at the moment of filing, whether the law admits a second credible reading and whether HMRC has expressed a view on it.

The analysis is easy while the transaction is live and nearly impossible to reconstruct convincingly two years later. Advisers who already write a short note on genuinely arguable positions are most of the way there.

A useful answer to a technical question stops being a single conclusion. It becomes: here is the position, here is the alternative reading, here is whether HMRC has said anything, and here is the source for each.

✅ In practice: That shape of answer is what GAIN Tax is built to produce. Each response is grounded in UK legislation, HMRC guidance and case law with the source shown against the point, so a second credible interpretation is visible rather than something you have to remember to go looking for. Our published benchmark records how often that holds: 93.2% correct across 250 questions in 21 UK tax domains, with 4.8% partially correct and 2.0% incorrect. We also publish what the tool will not do and where professional judgement remains yours.

• Identify clients where a single transaction could plausibly generate a £5m tax advantage. The list is usually shorter than expected and rarely who you assume.
• Adopt a light habit: on genuinely arguable positions, record the alternative reading and the reasons for rejecting it, at the time.
• Watch for the government response, and read it before assuming any of the above survived consultation intact.

The uncertain tax treatment regime was designed for a few hundred very large businesses. The consultation published in March proposes to extend it to individuals and trusts with no size filter, to five more taxes, to a new class of uncertainty defined by HMRC not having spoken — and to narrow the exemption that currently covers what HMRC already knows.

None of it is law. The consultation closed on 4 June 2026, the government response is awaited, and any legislation would apply to returns filed after 1 April the following year.

The habit it points towards is worth adopting regardless of what the response says. A contemporaneous note explaining why one credible reading was preferred over another costs a few minutes when the position is taken, and it is worth a great deal in an enquiry whether or not this proposal ever reaches the statute book.

For more on choosing tools that surface alternative readings rather than a single confident answer, see our guide to choosing AI tax research software in the UK, or browse the rest of the blog. If you want to test how this works on a live question, create a GAIN Tax account.

No. The current regime applies only to large companies and partnerships with turnover above £200m or a balance sheet total above £2bn, and covers corporation tax, VAT and income tax or PAYE. The extension to individuals and trusts is a proposal in a consultation that closed on 4 June 2026 and has not been legislated.

It is the tax advantage attached to the uncertain treatment, not a measure of the taxpayer's size or wealth. Under the current regime it sits alongside the large-business entry tests. Under the proposal, it would be the only filter for individuals and trusts, with no wealth, income or turnover test applied underneath it.

Notification would be required where more than one credible legal interpretation of the law exists and HMRC's view on the point is not known. This is aimed at uncertainties falling outside the two existing triggers, particularly involving novel products or processes with no HMRC guidance. Transfer pricing calculations would be excluded from this trigger.

The consultation proposes adding stamp duty land tax, national insurance contributions, construction industry scheme withholding obligations, capital gains tax and inheritance tax. These would join corporation tax, VAT and income tax including PAYE, which are already in scope.

The consultation proposes narrowing the general exemption. Today it applies where it is reasonable to conclude that HMRC already has the relevant information about the uncertainty. Under the proposal, it would apply only where the taxpayer has confirmation from HMRC that it is aware of the uncertainty, so a slow or ambiguous HMRC response would leave the notification duty in place.

A government response to the consultation is awaited. Any legislation would be introduced in the next available Finance Bill and would apply to returns filed after 1 April the following year, so the earliest practical application is well beyond the current filing season.

Identify clients capable of generating a £5m tax advantage on a single transaction, and start recording the alternative reading and the reasons for rejecting it whenever a genuinely arguable position is taken. The record is cheap to make at the time and valuable in an enquiry regardless of whether the regime is extended.