HM Revenue and Customs used the final week before the 5 October registration deadline to push side-hustle earners, landlords, and newly self-employed workers through an upgraded Self Assessment sign-up service, warning that missing the cut-off can delay Unique Taxpayer Reference letters and trigger failure-to-notify penalties.

Who must register this week

Anyone with untaxed income for the 2025–26 tax year who is not already in Self Assessment must notify HMRC by 5 October 2026. That includes new freelancers, people renting spare rooms above the Rent a Room relief threshold, partners with partnership income, and investors with dividend bills beyond the amounts reportable without a return. HMRC said more than 640,000 customers registered in the year to 31 March 2026, a figure officials expect to rise as gig platforms issue their first consolidated statements.

What changed on 9 September

The department relaunched its online registration journey to reduce dropped sessions when users verify identity through Government Gateway. HMRC claims the flow now surfaces clearer prompts for traders who should use the CWF1 self-employment form versus the SA1 form for other income. Users still receive UTR numbers by post within 10 working days for UK addresses, so waiting until 4 October risks missing the January online filing window even if registration technically succeeds.

Deadlines after you register

Paper returns for 2025–26 are due 31 October 2026; online returns and balancing payments land 31 January 2027. Payments on account follow the usual 31 July schedule for those already inside the system. HMRC reminded customers who stopped filing during 2024–25 that they must reactivate accounts before starting 2025–26 returns, a step accountants say trips people who assumed a quiet year meant permanent exit.

Penalty mechanics

Registering after 5 October does not always end the obligation—HMRC may issue a different filing deadline three months from its notice—but tax remains due by 31 January 2027 regardless. Failure-to-notify penalties scale with tax owed and can be backdated to when liability first arose. Late filing triggers an automatic £100 fine even if no tax is due, a surprise for hobby traders crossing the registration threshold for the first time.

Accountant capacity crunch

Firms across London, Manchester, and Birmingham report full October onboarding slots, pushing DIY registrants toward HMRC's checking tool before calling advisers. The tool asks about employment, pensions, property, and foreign income; it does not replace advice on allowable expenses but stops obvious double registration. Agents using HMRC's agent services must link authorisations before they can file, another reason to start this week.

Digital pain points

HMRC's identity verification partner backlog cleared after spring, yet accountants still see intermittent Government Gateway lockouts when users mix personal and business profiles. Keeping a dedicated email for tax correspondence and saving PDF proofs of registration timestamps helps if disputes arise. Making Tax Digital for income tax remains on the horizon for mandated digital records; registering now at least secures UTR access before those rules widen.

Practical checklist for Monday

Run the online checker, gather National Insurance numbers and business start dates, choose CWF1 or SA1, and screenshot confirmation pages. If you expect to file on paper, post SA1 immediately because postal delays eat the October filing window. Tell HMRC promptly if you no longer need a return—ghost expectations generate penalties even when income fell away.

Platform income statements

Ride-hail, delivery, and marketplace platforms began issuing annual summaries aligned with tax years this summer. HMRC's improved registration flow asks whether income arrived through apps so it can pre-select the right follow-up questions. Accountants urge users to download CSV ledgers now because platforms sometimes archive prior-year data after December, complicating January filings.

Student and overseas angles

International students who took paid internships in Britain may need returns if tax was not withheld at source. Double-tax treaties do not remove the registration duty—only the calculation. Students leaving the UK after graduation should close Self Assessment accounts formally to stop expected returns piling up while they are abroad.

Agent authorisation

If you hire an accountant, submit form 64-8 or use the digital agent authorisation service before 5 October so advisers can file on day one of the online window. Agents cannot backdate registration if clients miss the notify deadline; they can only help mitigate penalties with reasonable excuse evidence such as hospitalisation or HMRC service outages documented on status pages.