HMRC penalty letters explained: what every dormant-company letter actually means

By Ben Davies · Updated 5 October 2026

If you have just opened an HMRC letter and your stomach is in your mouth — this guide is the reference. It catalogues every common piece of HMRC correspondence a dormant UK company can receive, what it actually means, what HMRC wants you to do, and how serious it is.

For the broader "I got a letter — calm me down" piece, see HMRC letter about your dormant company: what to do. This guide assumes you know you have a letter and you want to know what kind.

How to identify which letter you have

HMRC letters carry a reference code in the top-right corner. Common codes for dormant-company correspondence include:

• CT603 — Notice to deliver a Company Tax Return
• CT208 — Reminder that the return is still outstanding, issued six weeks before the filing date
• CT41G — New company information form (issued shortly after incorporation)
• SA316 — Self assessment notice (usually a misdirected letter; not relevant for limited companies)

Late filing penalty notices are the exception — they are headed "Notice of penalty determination" rather than carrying a memorable form code. If your letter cites an accounting period and a penalty amount, that is what you have.

If you cannot find a reference code, look at the heading or subject line. HMRC letters almost always state their purpose in the first paragraph.

CT603 — Notice to deliver a Company Tax Return

What it is: HMRC's formal demand that you file a CT600 for a specific accounting period.

What it looks like: A letter or email saying "Notice to deliver a Company Tax Return" followed by an accounting period (e.g. "1 April 2025 to 31 March 2026").

What it means: HMRC is requiring a CT600 covering that period. The obligation is legal — you must file or be in breach of statutory duties.

How serious: Standard, and not a penalty. Be precise about what it is, though: the CT603 is the notice that creates the obligation, not a reminder about one. HMRC's actual reminder is a separate letter, a CT208, issued 42 days before the filing date where nothing has been paid and the return is still outstanding — which is every dormant company. Ignoring either triggers a late filing penalty once the deadline passes.

Deadline: 12 months after the end of the accounting period (the filing deadline). If you have tax to pay, the payment deadline is 9 months and 1 day after the end of the period, which is different.

How to respond:

1. Confirm whether the company is genuinely dormant for the period
2. If dormant, file a nil CT600 before the deadline — DormantFile files it
3. If it wasn't dormant but didn't trade and has no tax to pay — a loan being repaid, say — DormantFile files that return too. If it traded or has tax to pay, file a regular CT600 with an accountant
4. Once HMRC has accepted the return, the CT603 obligation is satisfied

Many dormant companies receive a CT603 every year. In a year with no notice, no return is due.

Late filing penalty notice — late CT600

What it is: A penalty for filing your CT600 late, or not filing it at all by the deadline.

What it looks like: A letter headed "Notice of penalty determination" or similar, citing your accounting period and a penalty amount.

What it means: You missed the filing deadline on the CT603, and HMRC has now imposed an automatic penalty.

How serious: Moderate. The penalties come in fixed steps:

• £200 — automatically issued the day after the deadline passes, for returns due on or after 1 April 2026 (£100 for returns due before then — the rate follows the deadline, not the filing date)
• A further £200 — if the return is more than three months late
• 10% of the unpaid tax — at six months late, HMRC estimates your Corporation Tax bill and adds 10% of the unpaid amount
• A further 10% — if the return is still unfiled at twelve months

If you file late three years in a row, the two fixed penalties rise to £1,000 each — or to £500 each where the return fell due before 1 April 2026, because that escalation sits behind the same commencement date as the £200. There are no daily penalties for a late CT600 — the £10-a-day regime you may have read about belongs to Self Assessment, not Corporation Tax.

For a nil return, the tax-geared penalties are 10% of zero — nothing. So a dormant company's real exposure is the fixed £400 per period (£200 + £200), or £2,000 per period if it is on its third consecutive late return — £200 and £1,000 respectively where the return fell due before 1 April 2026.

Deadline: None specific to the penalty notice itself, but the underlying CT600 is now overdue, and it moves into higher penalty bands until you file.

How to respond:

1. File the missing CT600 immediately — this won't cancel the penalty already charged, but it stops the return moving into the next penalty band
2. If the company was dormant for the period, check the penalty for grounds to appeal before you pay. Photograph the notice and we check your record for grounds and write the appeal letter — £9.99 a letter. The appeal window is 30 days from the date printed on the notice
3. Otherwise, pay the penalty within 30 days, or you may incur interest
4. If the missed filings span multiple years, file everything outstanding — DormantFile files each missed period

CT41G — New company information

What it is: The letter HMRC sends to every newly incorporated company, giving its 10-digit Corporation Tax Unique Taxpayer Reference (UTR).

What it looks like: A letter addressed to the company at its registered office, quoting the UTR and asking you to tell HMRC when the company becomes active.

What it means: HMRC has set up your Corporation Tax record. It needs to know when (if at all) you start trading.

How serious: Standard. Ignoring it can mean HMRC defaults your trading start date and your accounting period — potentially creating a mismatch with what you intend to file.

Deadline: Within 3 months of the company becoming active (starting to trade or otherwise coming within the charge to Corporation Tax) — not 3 months from incorporation. HMRC is often flexible if you respond before the first accounting period ends.

How to respond:

1. Keep the letter — the UTR on it is the company's Corporation Tax reference for good
2. If the company has started trading, tell HMRC, with your actual trading start date
3. If the company is dormant, watch for a CT603. A notice to deliver a return has to be answered, even for a dormant period, and DormantFile files the nil return

Penalty mitigation — when HMRC will reduce penalties

HMRC will sometimes mitigate or remove penalties, particularly for first-time offenders, fully-nil situations, or where there is a "reasonable excuse". Acceptable reasons include:

• Serious illness affecting the director
• Bereavement
• Unexpected hospital stay
• HMRC service failure (e.g. you tried to file but the HMRC API was down)
• Software failure (where you can document attempting to file on time)

What does not count as a reasonable excuse:

• You forgot
• You did not know you had to file
• You did not receive the CT603 (HMRC takes the position that posting it is sufficient delivery)
• Your accountant failed to file on your behalf
• You could not afford to pay

An appeal has to reach HMRC within 30 days of the date printed on the penalty notice, with the evidence behind it.

If the company was dormant for the period

A dormant company has a route that has nothing to do with excuses. Where the company was outside the charge to Corporation Tax for the whole period — no trade, no income of any kind including bank interest, no chargeable gains — an appeal can ask HMRC to record the period as dormant, withdraw the notice to deliver a return for it, and discharge the penalty on that basis. This is HMRC's own practice for a company outside the charge, and it is the argument worth making where it is true.

Two things matter. The appeal window is 30 days from the date printed on the notice — that printed date starts the clock, not the day the letter reached you. And the argument is never that no return was due: once HMRC has issued a notice to deliver, a return is due, which is why filing the nil return as well as writing the letter is what makes the position tidy. Our guide to appealing an HMRC late filing penalty for a dormant company works through the whole route. Photograph the notice and we check your record for this ground and write the letter — the check is free, and the letter is £9.99. An appeal is a request: the decision is HMRC's.

What to do if you have multiple unfiled years

If you have ignored CT603 notices for multiple years and are now staring at a stack of penalty notices, the priorities are:

1. Stop the bleeding. File the oldest overdue CT600 first, then work forwards to the present. Every period you file stops that return moving into the next penalty band.
2. Bring everything current. File every outstanding period, including the current open one.
3. Check each penalty for grounds. Photograph each penalty notice and we check whether the company was dormant for that period — the ground our appeal letter makes. Each notice has its own 30-day window, from the date printed on it.
4. Set up reminders for the future. Subscribe to a calendar feed of deadlines so you do not repeat the situation.

DormantFile files outstanding CT600s for any historical period the company existed for. There is no separate "catch-up" mechanism — you just file each missed period as a nil return.

Letters you might receive that are NOT about your dormant company

Some letters look like they are about your dormant company but are actually about something else:

Self assessment letters (SA316, SA300, etc.) — These are for personal tax returns, not limited companies. If you receive one in the company's name, it is usually a misdirected letter. Check the addressee carefully. (One related point: if you file a personal return yourself, from 2025/26 your dormant directorship must be declared on it — see the new SA102 rules.)

VAT correspondence — If your company is not VAT-registered, any VAT letter is either a mistake or someone using your company name on a VAT return. Check Companies House for company names similar to yours.

PAYE correspondence — If your company is not registered as an employer, PAYE letters should not be addressed to it. Same advice: verify the addressee and the company name.

Companies House letters — These come from Companies House, not HMRC. Common ones include strike-off warnings, confirmation statement reminders, and accounts overdue notices. They are separate from any Corporation Tax matter.

When to use a professional

Most dormant-company HMRC letters come down to a nil return, which DormantFile files, or a penalty, which our appeal letter can argue where there are grounds. Get professional help (accountant or tax adviser) if:

• HMRC has opened a formal enquiry into the company (an enquiry opens with a written enquiry notice under Schedule 18 of the Finance Act 1998, typically followed by information requests)
• The company has some trading history that you are not sure about — there may be tax due
• You are reactivating the company to trade again

Key points

• Most HMRC letters about Corporation Tax carry reference codes (CT603, CT41G). The code tells you exactly what the letter is; penalty notices state their purpose in the heading instead.
• A CT603 is HMRC asking you to file a CT600 — the notice that creates the obligation, not a reminder. The reminder is the CT208, six weeks before the filing date.
• A late filing penalty notice means you missed the CT600 deadline. For a nil return the exposure is £200, rising to £400 past three months — £1,000/£2,000 for a third consecutive late return. Where the return fell due before 1 April 2026 the previous rates apply instead: £100 rising to £200, and £500/£1,000 for a third consecutive late return. There are no daily penalties.
• A CT41G is HMRC setting up your Corporation Tax record and giving you the company's UTR. Keep it, and tell HMRC when the company becomes active.
• Penalties can be mitigated for genuine reasonable excuses, but "I forgot" or "I didn't know" do not count.
• If you have multiple unfiled years, file everything outstanding first, then check each penalty for grounds to appeal.
• Letters about VAT, PAYE, Self Assessment, or Companies House matters are not Corporation Tax letters and need separate handling.

If you need to file a nil CT600 or a stack of missed ones, DormantFile generates compliant returns for any historical period and submits them directly to HMRC. See how it works for the full flow.

For more on CT600s, dormant tax obligations, and HMRC correspondence, the CT600 hub collects every relevant guide, answer, and tool on this site.