I'm an Estate Planner Offering an Estate Administration Service. Do I need to register with HMRC as a Tax Adviser?

I've had the same conversation with several clients over the past couple of weeks, and I suspect the problem they're running into is about to catch a lot more estate planning and probate firms out.

Each of them went to register with HMRC as a tax adviser - correctly, because the nature of their work requires it - and hit the same wall. You cannot apply for an Agent Services Account without evidence of AML supervision. No supervisor, no supervision number, no account. And without the account, you cannot legally interact with HMRC on a client's behalf.

None of these firms had thought of themselves as needing this. They're estate planners and probate practitioners. They don't do tax returns for a living, they don't call themselves accountants, and they don't think of themselves as being classed as tax advisers. But HMRC's definition doesn't ask what you call yourself. It asks what you do.

What is a Tax Adviser?

HMRC is explicit about this:

"If you interact with HMRC about someone else's tax affairs and get paid for it, we consider you to be a tax adviser. This means you'll need to register for an agent services account."

'Interaction' with HMRC includes phone, post or email, messages through the GOV.UK website or the HMRC app, making payments, and sending returns, claims or other documents on behalf of clients.

Consider your typical week of estate administration. Submitting an IHT400 in relation to an estate on behalf of a client. Corresponding with HMRC about an estate's tax position and whether it's entitled to an exemption or relief. Making a payment on account of inheritance tax. Chasing a query on a client's behalf. If any of that is part of your paid work, you are, in HMRC's eyes, a tax adviser - regardless of your job title, your professional background, or how you've always described your business.

This isn't a new interpretation designed to catch people out. It's simply that mandatory registration is now being enforced in a way that exposes a gap a lot of companies didn't know they had.

HMRC is rolling out mandatory tax adviser registration - Modernising and Mandating Tax Adviser Registration (MMTAR) - in phases:

Window	Who it applies to
18 May – 18 August 2026	New tax advisers, or advisers interacting with HMRC without an existing Agent Services Account, Self Assessment or Corporation Tax account
18 August – 18 November 2026	Advisers with a Self Assessment or Corporation Tax account, but no Agent Services Account
18 November 2026 – 18 February 2027	Advisers who solely provide payroll services
31 December 2026 – 31 March 2027	Those who already hold an Agent Services Account, and financial services organisations

If you've never registered with HMRC as an agent before - which describes most estate planning and probate firms - you're almost certainly in that first window. It closes on 18 August 2026. As I write this, that's under two weeks away.

Miss it, and you risk restrictions on your ability to interact with HMRC for clients, and potential penalties if you carry on regardless. For a firm mid-way through administering someone's estate, that's not an abstract compliance risk. It's the difference between being able to do the job you've been instructed to do for a family - and not.

The Chicken-And-Egg Problem

Here's where it gets even trickier. Registering for an Agent Services Account is meant to be the straightforward bit – an online form, in theory. But HMRC won't let you complete it until you can show you're supervised for anti-money laundering purposes, with a supervisor and a supervision number attached to the application.

For firms that have never thought about AML supervision before, that's not a box you can tick in an afternoon. You need to have everything in place to be able to register, apply and have this approved – all before you can even start the ASA application. And AML registration has its own processing time (currently stated to be 'up to 45 days'), so leaving it until the last two weeks before the 18 August deadline is not a safe plan.

This is precisely the situation I mentioned above: firms discovering, partway through applying for something they now know they need, that there's a second, unfamiliar requirement standing between them and it.

Why Estate Planners and Will Writers Fall Through the Gap

Solicitors and licensed conveyancers have a professional body that supervises them for AML and reports that supervision to HMRC automatically. Accountants generally sit under a recognised accountancy body. Will writers and estate planners who aren't solicitors - a large and growing part of the sector - don't have that automatic cover. If no professional body is supervising you, the responsibility for AML supervision usually falls to HMRC directly, and it doesn't happen on its own. You have to register for it.

That's the structural reason this keeps catching firms out. It's not carelessness. It's that the sector has grown a category of firm - estate planner, probate practitioner, will writer - that doesn't sit identifiably in any of the professions AML supervision was originally built around. The rules have caught up. Awareness in the sector hasn't, yet.

What To Do Now, Not Later

If you assist clients with any part of the estate administration process and you haven't checked your AML supervision status or your Agent Services Account, here's what to do now:

• Establish whether you're currently supervised for anti-money laundering purposes, and by whom. If you're not sure, that's the first thing to resolve - not the Agent Services Account application.

  
  

• If you don't have a supervisor, look at your options and register. Build in time for processing; it's not instant.

  
  

• Once supervision is in place, apply for your Agent Services Account with your supervisor and supervision number to hand.

  
  

• Check which MMTAR window applies to you, and don't assume you have until 2027. If you've never registered as an agent before, the first deadline - 18 August 2026 - is very likely the deadline that applies to you.

Do not wait until you're in the middle of administering an estate for a grieving family to find out you can't do the work you've been instructed to do. That's the worst possible moment to discover a gap in your compliance, both for you and for the family relying on you.

Next Steps

If you're not sure where you stand, WillComply is here to help. We have built the WillComply AML Compliance Pack for will writers, estate planners and probate firms to help you get supervision-application ready. Get the WillComply AML Compliance Pack

Any questions? Contact us