Whoever does your books now has to register with HMRC. You cannot look them up

On 18 August the first deadline passed in a change most business owners have not heard of: mandatory registration for tax advisers. Anyone who is paid to deal with HMRC about somebody else's tax now has to be registered with HMRC to do it, and the requirement is arriving in waves through to next spring.

The word "adviser" undersells who is caught. HMRC's own fact sheet says the rule applies regardless of job title, to anyone paid to interact with HMRC on a client's behalf. Phoning HMRC about your PAYE counts. Emailing counts. Filing your return through accounting software counts, because HMRC treats a submission through software or an API as an interaction like any other. If somebody invoices you for doing any of that, this is about them.

And here is the part that makes it your problem rather than theirs: the filings are yours. If the person who submits your return is no longer permitted to interact with HMRC, what actually happens is that your return does not get filed, and the deadline it misses has your name on it, not theirs.

Who has to register, and when

The rollout runs in four windows, each three months long:

0118 May to 18 August 2026: advisers who had no agent account with HMRC at all
0218 August to 18 November 2026: advisers with a Self Assessment or Corporation Tax account but no agent services account
0318 November 2026 to 18 February 2027: payroll-only providers
0431 December 2026 to 31 March 2027: financial services organisations

An established firm that already holds an agent services account does not register again. HMRC moves those firms onto the new system by 31 March 2027 and contacts them through the account if it needs anything.

Read that list again and notice who the first window was for. Advisers with no agent account are the informal end of the market: the person who does the books for a dozen small firms, deals with HMRC by phone and post, and has never appeared in any HMRC system as an agent. That is exactly the corner where the good and the questionable sit side by side and look identical. More than 4,000 applications went in during the first window. The interesting number is the one nobody has: how many people who should have applied did not.

Registration itself is free, done online, and takes about an hour. There is one prerequisite worth knowing about because it is a useful tell: an adviser has to have their anti-money laundering supervision in place before HMRC will accept the application. Every legitimate bookkeeper and accountant already has this. One who cannot register because of it was operating outside the rules before this scheme existed.

There is no register for you to check

You would expect a registration scheme to come with a public register. This one does not. There is no page on GOV.UK where you can type in your accountant's name and get a tick. The checker HMRC built is for advisers wondering whether they need to register, not for clients wondering whether theirs did.

So the only check available is the direct one: ask. It is a one-line email, and the answer tells you a lot either way.

A good answer sounds like one of these. "We already hold an agent services account, so we're not in the registration waves." Or: "our window runs to 18 November and our application is in." Or simply a registration number. Any of those, given without hesitation, and you are done.

A worrying answer is a pause, a change of subject, or "that doesn't apply to us" from somebody who files things on your behalf. It might still be innocent. But HMRC has said that advisers who carry on unregistered after their window closes face being stopped from acting, and financial penalties and bans if they persist. You do not want to discover which category your bookkeeper is in during the last week of January.

One more thing to expect: email about this, some of it genuine and some of it not. A new government scheme with deadlines is raw material for fakes, and we wrote about how to judge a message claiming to be HMRC when MTD created the same conditions. The rule holds here. Never act on the message; go to GOV.UK yourself, or ring your adviser on the number you already had.

The question behind the question

Strip the news away and this is a familiar audit: who is authorised to act for your business, and would you know if that changed?

Most owners can not say, off the top of their head, which agents currently hold authority over their PAYE, their Corporation Tax and their personal return. Authorisations from an accountant you left years ago have a way of surviving the relationship. Your HMRC business tax account lists who is authorised against each tax; reading that list takes five minutes and belongs in the same drawer as checking who actually owns your domain name. Same principle, different login: the assets and authorities that matter to your business, held where you can see them.

We are on both sides of this one. We build the systems that talk to HMRC, Xero and Companies House for our sister practice, Opus Accountancy, so we see what agent authorisation looks like from the software end, and we spend the rest of the week helping firms work out who holds the keys to what. If you want a second pair of eyes on the list of people and systems authorised to act for your business, ask us. The good outcome, as ever, is that we tell you it is already in order.

We work with businesses across Knutsford, Alderley Edge, Wilmslow, Altrincham, Stockport and Warrington, and remotely for clients anywhere in the UK.