The dates are set. The details aren't.
From 18 May 2026, tax advisers who interact with HMRC on behalf of clients must register through a new agent services account (ASA) system. HMRC published guidance on 18 February confirming the timeline, but practitioners are still waiting for substantive implementation detail.
The rollout runs in stages: general registration from 18 May, Self Assessment and Corporation Tax holders from 18 August, payroll-only providers from 18 November. Advisers get a three-month grace period after each deadline to register before HMRC stops accepting interactions.
Who's caught
The Finance Bill 2025-26 defines 'tax adviser' broadly: any firm or individual interacting with HMRC on a client's behalf for payment, whether by phone, post, email, or GOV.UK. This covers accountants, bookkeepers, tax consultants, and anyone submitting returns or corresponding with HMRC commercially.
Existing ASA holders don't re-register, but must verify they meet conditions when HMRC contacts them. No word yet on when that contact happens. ICAEW flagged this gap publicly.
The conditions
Firms need current AML supervision and clean tax compliance (no outstanding returns or unpaid taxes). Small firms (five people or fewer) must register all staff as 'relevant individuals'. Firms with six or more nominate five key people plus directors and senior managers.
Non-compliance blocks HMRC interaction. Consequences escalate: notices to cease advising, financial penalties, or permanent bans from representing clients.
What's missing
The ATT and CIOT published FAQs to fill gaps in HMRC's guidance. Professional bodies want clarity on how existing ASA holders transition, what 'interaction' means in edge cases, and how nomination requirements apply across different firm structures.
The Solicitors' Law Society called for refinement to avoid unnecessary burdens on already-regulated providers. Finance Bill clauses 220-246 are under review, but implementation starts in eleven weeks.
HMRC promised further updates. Advisers are waiting.