HMRC Tax Adviser Registration Tranche One Closed 18 August

Today — 18 August 2026 — is the hard close for HMRC’s first Modernising and Mandating Tax Adviser Registration (MMTAR) window. New tax advisers, and advisers who interact with HMRC without an Agent Services Account (ASA), Self Assessment agent account, or Corporation Tax agent account, must finish applications before the portal clock turns over. The same Monday opens the three-month tranche-two window (18 August to 18 November 2026) for advisers who already hold SA or CT agent accounts but still lack an ASA.

HMRC’s July press release warned that missing a relevant registration deadline can delay or disrupt client services, and that continuing to act after HMRC instructs you to stop may attract sanctions including financial penalties. Treat today as an application day, not a planning day: submit complete evidence packs, confirm which tranche you are in with the GOV.UK checker, and diary tomorrow’s MFA activation separately.

If you are still in tranche one

You are in tranche one if you are a new tax adviser, or you interact with HMRC on clients’ tax affairs without an ASA and without SA or CT agent accounts. Anyone paid to interact with HMRC on behalf of someone else about their tax affairs is generally treated as a tax adviser unless an exemption applies — use HMRC’s interactive checker rather than assuming you are out of scope.

Advisers who already hold an ASA do not re-register in this phase; HMRC will contact them through the ASA if further information is needed when they move onto the new digital system. Payroll-only firms sit in a later window (18 November 2026 to 18 February 2027) and should not confuse that timetable with today’s close.

Tranche two opens today for SA/CT-without-ASA firms

From today through 18 November 2026, advisers with a Self Assessment or Corporation Tax agent account but no ASA must register for an ASA. HMRC’s MTAR manual confirms you can continue interacting with HMRC for clients during the three-month application window and while HMRC considers a timely application — incomplete packs still create later access risk.

Day-one priorities: confirm identity evidence, AML supervision status, supervisory body details, and named owners for every agent ID across offices. Do not assume a sibling account already carries an ASA. Keep the weekend tranche-two checklist beside the application form so partners are not inventing evidence lists under client pressure.

Action checklist for 18 August

Run HMRC’s GOV.UK checker and record which tranche you are in — tranche one close today, tranche two open today, or later payroll/ASA cohorts.

Submit any unfinished tranche-one ASA application with complete supporting evidence before end of 18 August 2026.

Open tranche-two ASA applications for SA/CT-without-ASA firms and map agent IDs so nobody is left off the register.

Keep MFA activation (19 August for voluntary opt-ins) and the third-party data consultation close (20 August) as separate named workstreams — three deadlines in three days.

How FinnAccountings helps while registration beds in

Clean client ledgers reduce pressure when partners spend Monday on ASA applications. FinnAccountings helps Ireland and UK advisers and business owners prepare bookkeeping and tax packs with Chartered Accountant insight before you or your ICAEW/ACCA or Chartered Accountant (Ireland) adviser files. Start a free trial for review-ready drafts — we prepare records; we do not register you with HMRC or file agent applications on your behalf.

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Related reading

Use yesterday’s final-day briefing for the fuller tranche-one narrative, then the weekend tranche-two checklist if you open ASA applications today.

MMTAR tranche one final day (17 Aug) →

Tranche-two firms should keep the weekend ASA prep checklist beside the application form.

MMTAR tranche-two weekend checklist →

Tranche-two firms should start with today’s day-one ASA briefing after the close.

MMTAR tranche two: day one after 18 August →