HMRC has restarted automatic Corporation Tax late-filing penalty notices. That is not a quiet systems footnote. It is the moment when the doubled fixed penalties that took effect for filing dates on or after 1 April 2026 start landing in company mailboxes and agent portals — including for returns that went late while notices were paused.
Primary sources: Agent Update Issue 146 (the formal resume notice), the policy paper on increases to Corporation Tax late filing penalties, the detailed increases to CT late filing penalties table under Schedule 18 Finance Act 1998, HMRC’s Corporation Tax for companies guidance, file your Company Tax Return rules, and ATT’s earlier note that automatic CT penalty notices were temporarily paused while systems were updated.
If you run a UK group, PE holdcos, SPVs or a long tail of dormant/nil-liability companies, treat this as a live cash and governance event — not a “note for the tax team.”
What Agent Update 146 actually said
In Issue 146 of Agent Update, HMRC confirmed three operational facts:
1. From 1 April 2026, late filing penalties for Corporation Tax increased.
2. HMRC updated the CT system so the correct (higher) amounts would print on notices, and temporarily paused automatic penalty notices so customers would not receive letters showing the old figures.
3. The system updates are now complete, and automatic notices are being issued again.
Companies that file after the deadline remain liable at the increased rates. Further penalties can still stack if the return stays outstanding. Some clients who filed late may receive notices later than usual while HMRC works through the backlog.
HMRC’s client messages are blunt: keep filing on time; you remain liable even if no notice arrived during the pause; do not contact HMRC merely because a notice was delayed. Bloomberg Tax reported the same restart in mid-August. The pause delayed letters, not liability.
The new fixed rates — lock these in the board pack
Under the increases TIIN, fixed penalties under Schedule 18 FA 1998 for returns with a filing date on or after 1 April 2026 are:
- Return late: £200 (was £100)
- Return more than 3 months late: £400 (was £200)
- Three successive failures, return late: £1,000 (was £500)
- Three successive failures, return more than 3 months late: £2,000 (was £1,000)
Policy rationale: the fixed amounts had sat unchanged since 1998; nearly 30 years of inflation left them worth roughly half their original real value. Budget 2025 restored that bite. Exchequer scoring: +£45m in 2026–27, rising toward +£70m by 2030–31.
These are fixed penalties. They apply whether or not any Corporation Tax is due. Dormant companies, loss-makers and pure holding vehicles still pay if the CT600 is late — the tax line can be nil and the penalty line still hurts, especially on three successive failures.
Tax-geared penalties (typically 10% of unpaid tax at six and twelve months) sit on top and were not rewritten. Late payment interest remains a separate cash cost.
Filing date vs payment date — stop conflating them
A Company Tax Return is normally due 12 months after the end of the accounting period. Corporation Tax is normally due earlier — 9 months and 1 day after the end of the accounting period for companies outside the quarterly instalment regime.
The penalty restart is about the return. A paid-up company with a late CT600 still takes the fixed filing hit. An on-time return with late tax still attracts interest. Your close calendar needs both clocks visible.
For groups, the failure mode is familiar: accounts slip, audit slips, CT600 slips, and someone assumes “HMRC has not written, so we are fine.” Agent Update 146 ends that assumption.
Why the pause created a false sense of calm
When HMRC paused automatic notices, many teams treated silence as comfort. ATT’s May note already warned that late filers remained liable at the increased rates. The pause was IT hygiene so HMRC would not mail pre-increase amounts — never a holiday from Schedule 18.
Any entity that filed late for a filing date on or after 1 April 2026 may now receive a higher-rate notice later than usual. Budget for backlog letters across subsidiaries and SPVs, agent-portal noise, and escalation where three successive failures are already in play. If you have a PE portfolio or UK holdco stack, run a filing-status sweep now.
What every CFO should lock this week
1. Entity filing register. List every UK company in scope for CT600s. Accounting period end, filing deadline, owner, last three filing outcomes. Flag any entity already on a successive-failure path toward the £1,000 / £2,000 band.
2. Dormant and nil-liability entities. Confirm whether a return is still required and whether the CT600 is in the diary. A £200 or £400 fixed penalty on a shell company is still a control failure at the next investment committee.
3. Close-to-file workflow. Map trial balance → accounts → tax computation → CT600 submission. Put a hard internal gate at least 30 days before the statutory filing deadline for material entities.
4. Agent SLA and portal monitoring. Require written confirmation of submission date and receipt. Check HMRC online services for outstanding returns and new penalty notices as the backlog clears.
5. Board and investor narrative. For PE-backed groups, one slide: “CT filing penalties doubled from April 2026; automatic notices resumed (Agent Update 146); group exposure and remediation.”
6. Appeal discipline. If a notice arrives and there is a genuine reasonable excuse or processing error, document facts immediately and follow the appeal route on the notice. Payment does not cure a late return.
7. Do not phone HMRC just to ask where the letter is. Use that energy on the entities still open.
How this sits next to the rest of the stack
Agent Update 146 did not only restart CT penalty notices. The same issue pushed mandatory payrolling of benefits in kind preparation (phase 1 from April 2027), P800 season through November 2026, GfC19 short-term business visitors, the temporary VAT reduced-rate unwind, Customs Modernisation call for evidence (open to 15 September 2026), and CBAM prep for 1 January 2027.
CFOs who only chase the shiny consultation will miss the boring cash event already in flight: fixed CT penalties at double the old rates, with the letter factory switched back on. Keep Companies House accounts filing separate — late accounts have their own civil penalty regime, and cleaning one deadline does not clean the other. See also HMRC’s practical Company Tax Return guidance when you refresh process notes.
Portfolio and PE angle
In a buy-and-build or multi-SPV structure, CT600 hygiene is diligence and value protection: test the last three filing cycles on entry; put CT filing KPIs next to VAT and PAYE on hold; expect buyers to price repeated late filing as weak control on exit; and keep holdcos and incentive vehicles on time — “we only care about the OpCo” is how holdco penalties accumulate.
Bottom line
The law moved on 1 April 2026. The letters moved when Agent Update 146 confirmed automatic notices had resumed. Liability never paused. Lock the £200 / £400 / £1,000 / £2,000 grid, sweep every UK entity, separate filing clocks from payment clocks, budget for backlog notices, and stop reading HMRC silence as comfort — the system is posting again.