If Your Accountant Files Your Tax Return, This 31 July Deadline Affects You Too

HMRC is rolling out mandatory multi-factor authentication (MFA) across every agent account — the login accountants and tax agents use to manage your Self Assessment, VAT and PAYE on your behalf. If you rely on an accountant, bookkeeper or tax adviser, a short window is closing that could affect how smoothly your affairs get handled this autumn.

What's actually happening

HMRC confirmed in June 2026 that MFA will be switched on across all agent accounts between 28 September and 15 October 2026, as a security upgrade in response to rising online fraud targeting agent logins. The rollout has three phases: two voluntary opt-in windows over the summer, then a mandatory switch-on for everyone left. Agents who apply by 30 June 2026 got MFA activated on 15 July; agents who apply by 31 July 2026 will have it activated on 19 August. Miss both voluntary windows, and the account is switched over automatically in the autumn phase regardless.

Why HMRC is doing this

Agent accounts are an attractive target for fraudsters because a single compromised login can expose dozens or hundreds of clients' tax records and repayment claims. HMRC says the change is designed to "add an extra layer of security" against evolving online threats, following similar security upgrades already applied to individual Personal Tax Accounts.

What this means if you use an agent

You won't personally need to set up MFA — that's the agent's login, not yours — but a poorly prepared handover can cause delays if your accountant is locked out of your file at a busy point in the tax year, particularly with the first Making Tax Digital quarterly deadline having landed on 7 August 2026 for many sole traders and landlords.

Checklist: what to ask your accountant now

• Ask whether their practice has already opted in to MFA, or is waiting for the mandatory autumn switch-over.
• Confirm they have a registered mobile number or authenticator app ready for their HMRC agent account — MFA typically requires a second device to approve logins.
• If you have a Self Assessment or VAT deadline falling in late September to mid-October, ask your accountant to complete any pending filings before the mandatory MFA switch-on window to avoid last-minute access issues.
• If you file your own return through a personal Government Gateway account rather than an agent, this change does not directly affect you, but it's still worth confirming your own account has up-to-date recovery details.
• Keep a copy of any documents or figures you've sent your accountant recently, in case there's a short access disruption during the transition.

Key Numbers

• Voluntary opt-in 1 deadline: 30 June 2026 (activation 15 July 2026)
• Voluntary opt-in 2 deadline: 31 July 2026 (activation 19 August 2026)
• Mandatory rollout window: 28 September – 15 October 2026
• First MTD quarterly update deadline (sole traders/landlords over £50k): 7 August 2026

Sources

• ICAEW: HMRC's 31 July deadline approaches in roll-out of MFA
• ICAEW: HMRC sets timetable for agent multi factor authentication rollout
• Chartered Institute of Taxation: HMRC confirm timetable for MFA rollout
• Ross Martin: SME Tax Update 23 July 2026

Educational content only — not financial advice.