An HMRC nudge letter is a letter sent to a group of taxpayers HMRC believes share a particular risk, rather than a check opened into you individually. HMRC calls this the One to Many approach. It is not a formal compliance check, and the letter itself carries no legal obligation to reply unless HMRC has separately opened a check. If a One to Many letter asks you to provide information or records, HMRC must either open a formal compliance check under the normal procedure or state clearly that the request is voluntary.

Nudge letters unsettle people because they look official, they are official, and yet they sit outside the formal enquiry machinery. Understanding which of those two things you are holding decides what you do next.

What One to Many actually is

HMRC defines the One to Many approach as a single, common approach to more than one customer, designed to influence behaviour and promote compliance. It is a campaign, not a case.

Delivery can be by post, through digital channels such as personal tax accounts, email or SMS, or through agents and other intermediaries. The same letter goes to everyone in the selected population. You have been selected because you match a risk profile, which is not the same as HMRC having found something in your return.

How to tell a nudge letter from a formal enquiry

A formal compliance check is opened under a specific statutory power and the letter will say so. A One to Many letter is a prompt to review your own position.

The critical distinction is what happens when information is requested. HMRC’s own guidance is that if a One to Many communication asks a customer to provide information or records, HMRC must either formally open a compliance check following the established procedure, or state explicitly that the request is voluntary and there is no obligation to respond. One to Many activity also excludes formal notices covered by legislation, such as a Schedule 36 information notice.

So the practical test is: does the letter cite a statutory power and tell you a check has been opened? If not, you are looking at a prompt.

Check the letter is genuine

HMRC-branded letters are a favourite of fraudsters. HMRC publishes a list of its genuine contact campaigns so that you can check whether a letter you have received is real before you engage with it or act on any contact details it gives. Verify first, using contact details you have found independently, not the ones printed on the letter.

What to do when one arrives

Do not ignore it. A nudge letter is HMRC telling you where it thinks the risk is. If there is nothing to correct, that is a short piece of work to establish and document. If there is something to correct, correcting it voluntarily is almost always a better position than waiting for HMRC to find it, because disclosure that is unprompted attracts more favourable treatment on penalties than disclosure that follows discovery.

Equally, do not over-respond. Sending HMRC a large volume of unrequested material in reply to a campaign letter can widen the ground rather than close it. Work out what is actually being asked before answering.

Speak to your accountant before you reply. This is the point at which the cost question arises, because reviewing a position properly is chargeable time.

Why HMRC uses them

Scale. HMRC collected 966.4 billion pounds in tax revenues in 2025 to 2026 and reported 50.2 billion pounds of compliance yield, the first time that figure has passed 50 billion. Campaign letters are a cheap way to move behaviour across a whole population without opening individual cases, and they are used heavily for exactly that reason.

Common questions

Is a nudge letter a tax investigation?

No. It is a One to Many campaign communication, not a compliance check opened into your affairs. HMRC can open a formal check afterwards, and how you respond to the letter can influence whether it does.

Do I have to reply to an HMRC nudge letter?

Not unless HMRC has opened a formal compliance check or issued a statutory notice. HMRC’s guidance requires it to either open a check under the normal procedure or state that the request is voluntary. Not being obliged to reply is not the same as it being sensible to stay silent.

How do I know the letter is really from HMRC?

HMRC publishes guidance listing its genuine contact campaigns. Check the letter against that list, and never use contact details taken from a letter you have not verified.

Will a nudge letter turn into a full enquiry?

It can. HMRC uses the response, or the absence of one, as part of its risk assessment. Reviewing the position properly and correcting anything that needs correcting is the way to reduce that risk.

Does tax fee protection insurance cover the cost of responding?

It depends entirely on the wording, and this is one of the areas where wordings diverge most, because a nudge letter is not a formal check. Read yours, and ask before assuming the review time is covered.

Related guides

This page explains what HMRC One to Many letters are. It is general information, not tax advice, and it does not describe the terms of any particular insurance policy.

Solar Insurance Services (Medway) Limited is registered in England and Wales, company number 05439438, and is authorised and regulated by the Financial Conduct Authority, firm reference number 459582.

Sources: HMRC Compliance Handbook CH600110 and CH600120 on the One to Many approach; HMRC guidance on checking whether a letter you have received from HMRC is genuine; HMRC annual report and accounts 2025 to 2026.