The brown envelope: what an HMRC enquiry actually involves

It is a formal check into a tax return you have already filed. First, HMRC gives you notice that it intends to enquire. That notice then opens the return for examination.

However, it is not an accusation of anything. Risk indicators prompt some checks, while others are simply random.

HMRC's compliance checks guidance collects the factsheets it issues at the start. Those factsheets tell you your rights as well as its powers.

HMRC also writes to your agent where you have one. So an accountant can pick the matter up without you forwarding everything twice.

Generally twelve months from the date you deliver the return, where you filed on time. HMRC guidance explains that the period for giving an enquiry notice runs up to 12 months from delivery.

Once that window closes, HMRC cannot open an enquiry into that return under those powers. The HMRC manual on the power to enquire sets out the rule.

So a return filed in October and untouched a year later usually sits beyond an ordinary HMRC enquiry. That is a real protection, and it rewards filing early.

Filing late changes the window. Where a return arrives after the filing date, the period runs from a different point, so check the dates carefully.

It is the route HMRC uses once the enquiry window has already closed. So an officer who concludes that you understated tax can assess the earlier year outside the normal process.

Discovery has its own time limits, and they depend on why the tax went wrong. The HMRC manual on discovery time limits sets them out.

Importantly, it is not a free pass to reopen anything. There are conditions, and taxpayers do challenge discovery assessments successfully.

Information and documents reasonably required to check your tax position, which is a broad test with real limits. In an ordinary HMRC enquiry that usually means bank statements, invoices, contracts and the workings behind a figure.

However, HMRC can issue a formal information notice where it does not get what it asks for. Penalties can follow a failure to comply with one.

Its powers are not unlimited. Certain documents stay protected, and requests must be reasonable. So replies deserve thought rather than speed.

Read it properly, note the deadline, and answer the question in front of you. The opening letter says which return it covers, which parts of it, and by when HMRC wants a reply.

Crucially, do not volunteer years or figures that nobody requested. Answering the question in front of you is not evasive; it is simply accurate.

In our practice we see enquiries widen because a well-meaning reply raised something new. Precision keeps a check small.

With a closure notice setting out the officer's conclusion, and often with nothing to pay. If nothing is wrong, the check simply ends and the return stands exactly as you filed it.

So if you overpaid, HMRC repays the difference with interest. If you underpaid, you pay the tax with interest, and a penalty may follow.

In practice, most checks we see end with a small adjustment or none at all. The letter is rarely the disaster it feels like on arrival.

Only when an inaccuracy came from more than an honest mistake. The level then depends on the behaviour behind it, and on whether you told HMRC about the problem before it asked you.

For example, a careless error attracts a lower range than a deliberate one. Coming forward unprompted reduces the penalty further, which is the whole logic of disclosure.

Notably, taking reasonable care is a defence in its own right. Keeping workings and evidence is what makes that argument available later.

Penalties can also be suspended in some careless cases, subject to conditions. Ask about that possibility rather than assuming a charge is fixed.

Yes, and there is a defined route for doing so. You can ask HMRC for a review by an officer who was not previously involved, or you can appeal to an independent tribunal instead.

The GOV.UK guidance on disagreeing with a penalty explains the steps and the deadlines. Those deadlines are short, so diary them when the decision arrives.

Similarly, reasonable excuse can apply to some penalties. It is a separate argument from whether the tax itself was right.

A review costs nothing to request. So it is usually worth taking before deciding whether to appeal further.

It can change your American figures, which is the step most people miss entirely. Foreign tax credits on a US return depend on the British tax you actually paid, so a British adjustment moves them.

If an enquiry increases your UK tax, the credit available on the American side may rise too. If it reduces your UK tax, a credit you already claimed may be too large.

Our guide to avoiding double taxation explains how the credits work. Either direction can mean amending an American return.

Usually months rather than weeks, although a narrow check can close quite quickly. The timetable depends on how much HMRC asks for, and on how promptly each side answers the other.

You can push it along. Answering in full the first time, rather than in instalments, typically saves a round of correspondence.

If it drags without progress, you can apply to the tribunal for a closure notice. That step is unusual, though it exists precisely because checks should not run indefinitely.

Often, yes, and in considerably more detail than most people assume it does. Financial information now moves between countries automatically, and British banks report the interest they pay you each year.

Consequently, unreported foreign income tends to surface eventually rather than never. Our guide to how HMRC knows about your income covers the data it receives.

So an enquiry into foreign income is rarely a fishing expedition. Assume the underlying data already exists.

No, because each notice covers only the return that it actually names. So an HMRC enquiry into one year does not, by itself, open the years on either side of it.

However, what emerges can lead to other years. Where the same error repeated, HMRC may raise discovery assessments for earlier periods within the relevant time limit.

So a single-year check is worth answering with the other years in mind. Consistency matters more than volume here.

Tell HMRC before it asks you. An unprompted disclosure attracts a lower penalty range than one made after a check begins, and it changes the tone of everything that follows.

Usually you can amend a recent return yourself within the amendment window. Older years need a disclosure instead.

Our guide to registering for Self Assessment covers getting into the system properly, which prevents a common category of problem.

Keep evidence of when you discovered the error. That timeline supports an unprompted disclosure if HMRC later asks about it.

Not always, although it frequently helps more than people expect it to. A straightforward query about a single figure is something you can usually answer yourself with the records to hand.

Where the check covers several years, foreign income, or a business, professional help usually pays for itself. HMRC writes to your agent as well as to you, which keeps both informed.

Fee protection insurance exists for exactly this, and many accountants also offer it. It is worth checking whether you already have it before engaging anyone.

Work through these in order from the day the letter arrives.

Keep every piece of correspondence together, including notes of phone calls.

Take an illustrative example: an American in Leeds files her return in September, and the following March HMRC opens a check into her foreign income.

First it asks for statements on two overseas accounts, then for the workings behind her foreign tax credit claim. She sends exactly that, with a short covering note.

The check then closes three months later with a small increase. She then amends her US return, because the extra British tax changes the credit available there.

The first is ignoring the letter. Deadlines pass, formal notices follow, and a routine HMRC enquiry becomes a penalty conversation.

The second is over-answering. Volunteering unrelated years or accounts usually invites questions nobody had asked.

The third is forgetting the American side. A change to your British tax can leave a US return that no longer matches reality.

The fourth is handling it by phone alone. Put the substance in writing, so that both sides work from the same record.

We handle enquiries alongside both returns through our UK Self Assessment service, including the knock-on effects for American credits. Often we deal with HMRC directly, where that is simpler for you.

If a letter has arrived, send it to us and we will tell you what it covers and what it does not, at a fixed fee agreed first. This article is general information, not personal tax advice; take advice on your own facts from a qualified adviser.