Does my firm need to register under the new MTAR rules? A Guide for Solicitors and other Legal Professionals

12 Aug 2026

Published in: Member News
If your firm ever contacts HMRC on behalf of a client, be that for filing a return, submitting SDLT forms, or discussing an estate’s tax position, you may need to register.

If your firm ever contacts HMRC on behalf of a client, be that for filing a return, submitting SDLT forms, or discussing an estate’s tax position, you may need to register.

The Finance Act 2026 introduced a new Mandatory Tax Adviser Registration (“MTAR”) regime. Under the new regime businesses that are paid to interact with HMRC on behalf of clients in relation to tax matters must register with HMRC and meet certain minimum standards. HMRC's guidance is clear that the rules extend beyond traditional tax advisers and can apply to many legal professionals. For many solicitors, the key question is not whether they hold themselves out as tax advisers, but whether they interact with HMRC on a client's tax affairs in the course of providing legal services.

All legal practices with any HMRC-facing activity should review the new rules and confirm whether MTAR registration is required. If so, they will also need to adhere to the conduct provisions included in the legislation.

Who Must Register?

Under the MTAR legislation, ‘tax advisers’ may not ‘interact’ with HMRC unless they are registered. Both terms are widely defined and will apply to many solicitors.

Interacting with HMRC includes:

  • Contacting HMRC by telephone, post or email;
  • Sending a message to HMRC through a website or internet portal;
  • Filing a return, claim, notice or other document with HMRC (whether electronically or otherwise);
  • Communicating with HMRC in any other way.

A ‘tax adviser’ is an individual or organisation that, in the course of a business carried on by it, assists other persons with their tax affairs. Assistance with tax affairs is provided if a person or organisation:

  1. Advise another person in relation to tax;
  2. Act or purport to act as an agent on behalf of the other person in relation to tax;
  3. Provide assistance with any document that is likely to be relied on by HMRC to determine the other person’s tax position.

Putting both definitions together, many routine activities for solicitors could bring them within the scope of MTAR, such as:

  • Acting as agent for a client.
  • Preparing or submitting documents on which HMRC may rely.
  • Filing returns, claims or elections.
  • Making tax payments to HMRC on behalf of clients.
  • Corresponding with HMRC regarding a client's tax position.

Common Legal Services That May Trigger Registration

1. SDLT and Conveyancing

A firm is likely to require registration where it:

  • Submits SDLT returns.
  • Communicates with HMRC regarding SDLT.
  • Pays SDLT to HMRC on behalf of clients.

Accordingly, many residential and commercial conveyancing firms will need to consider registration. MTAR applies for interactions with HMRC so Scottish solicitors dealing purely with LBTT and Revenue Scotland are not within scope, however, Scottish solicitors should consider other interactions they may have with HMRC as these may still be caught.

2. Probate, Estates and Inheritance Tax

Firms acting for executors or administrators may require registration where they:

  • Submit inheritance tax accounts (such as IHT400 returns).
  • Correspond with HMRC regarding inheritance tax liabilities.
  • Deal with HMRC enquiries relating to an estate.
  • Submit estate income tax returns or administration period tax returns.

3. Trust Taxation and Trust Registration Service Matters

Registration may be required where a firm:

  • Registers trusts on the Trust Registration Service (TRS).
  • Updates TRS records.
  • Corresponds with HMRC concerning trust tax affairs.
  • Prepares or files trust tax returns.

4. Stamp Duty and Stamp Duty Reserve Tax on Shares

Corporate and commercial solicitors may fall within scope where they:

  • Submit stamp duty forms.
  • Arrange stamping of stock transfer forms.
  • Correspond with HMRC Stamp Taxes regarding share transactions.
  • Make stamp duty payments on behalf of clients.

5. Corporate Transactions

Law firms involved in mergers, acquisitions, reconstructions or share reorganisations should consider whether they:

  • Submit tax elections or claims.
  • Correspond with HMRC regarding clearances.
  • Engage with HMRC regarding transaction-related tax matters.
  • Direct interactions with HMRC on behalf of clients may bring the firm within the regime.

Activities That May Not Require Registration

Registration is not triggered merely because a solicitor discusses tax consequences with a client.

For example:

  • Explaining SDLT rates or reliefs.
  • Advising on inheritance tax implications.
  • Discussing trust taxation.
  • Providing general tax guidance without corresponding with HMRC.

The key question is whether there is an interaction with HMRC in relation to another person's tax affairs.

Are There Any Exemptions?

Yes. Finance Act 2026 and the HMRC guidance contain various exclusions and exemptions.

Examples include certain:

  • Voluntary or unpaid assistance.
  • Assistance to friends and family outside a business context.
  • Insolvency practitioners acting in specific statutory capacities.
  • Certain in-house tax functions dealing only with their own organisation's affairs.

Registration Timetable

Registration is being introduced in phases. HMRC's manual sets out different registration windows depending on an organisation's existing relationship with HMRC and whether it already holds an Agent Services Account. Registration generally commenced from 18 May 2026, with later windows applying to certain categories of adviser.

HMRC have developed an online checker to help firms establish if they need to register and if so the deadline for doing so. Note the deadline could be as soon as 18 August.

Registration Requirements

The rules apply on a legal entity basis, so for larger organisations with multiple group entities it will be necessary to register each legal entity which acts as an agent. Each organisation should be appropriately supervised for anti-money laundering and will be subject to ongoing HMRC scrutiny of its tax affairs. An entity may be subject to suspension if it is seen to be non-compliant by HMRC.

In addition to legal entities (companies, LLP’s, Partnerships) the rules require the identification of ‘Responsible Individuals’ (RI’s). These are the people responsible for overseeing the provision of tax advice. RI’s will be subject to ongoing scrutiny from HMRC on their personal tax affairs and their organisation may have its registration suspended if they are deemed to be non-compliant.

Once registered an entity, its RI’s and staff must comply with the HMRC standard for agents when corresponding with HMRC.

Practical Steps for Law Firms

Legal practices should:

  1. Review all service lines that involve HMRC interaction.
  2. Identify whether staff submit returns, make tax payments or correspond with HMRC on behalf of clients.
  3. Determine whether registration is required.
  4. Identify any relevant individuals who must be disclosed.
  5. Check that the firm's AML supervision and compliance arrangements satisfy HMRC's conditions.

In addition to penalties for failing to meet MTAR requirements, firms may be subject to ‘naming and shaming’ publications and be required to notify their clients if their registration is suspended or they are determined to be ineligible for registration.


Submitted by Ritesh from MHA
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