If a company tax return is delivered on or before its filing date, HMRC normally has 12 months from the day it was delivered to open an enquiry. For a company in a group that is not a small group under the Companies Act 2006, the 12 months run from the statutory filing date instead, so filing early does not shorten HMRC’s window. A late or amended return follows the same quarter day rule whether or not the company is in a group.
Tax investigation insurance from £108.75 a year (£9.06 a month).Pays up to £100,000 of your accountant's fees if HMRC opens an enquiry. No excess. Buy online in a few minutes.
What is the normal enquiry window for a company tax return?
The rules are in paragraph 24 of Schedule 18 to Finance Act 1998. An officer may enquire into a company tax return by giving notice within the time allowed:
- Return delivered on or before the filing date: up to 12 months from the day the return was delivered (paragraph 24(2)).
- Return delivered after the filing date: up to and including the 31 January, 30 April, 31 July or 31 October next following the first anniversary of the day it was delivered (paragraph 24(3)).
- Return amended by the company: up to the same quarter day next following the first anniversary of the amendment (paragraph 24(4)).
HMRC’s Enquiry Manual at EM1510 says a notice is only given by a date if the company receives it by that date, so a notice posted on the last day is too late. The general rules for all taxes are in our guide to the enquiry window for tax returns. This page deals with the group rule and how late filing interacts with it.
Why are group companies treated differently?
Paragraph 24(6) says that for a company which is a member of a group other than a small group, the 12 month period in paragraph 24(2) starts not from the day the return was delivered but from the filing date. It was inserted by Finance Act 2007 with effect from 19 July 2007. The effect is that HMRC has the same deadline for every on time return in a larger group, however early each company files.
HMRC’s internal guidance at EM1514 recognises that this gives it longer than it needs in many cases. It tells officers that where it is practical they should aim to open any enquiries into a group’s returns within 12 months of the delivery of the last return from any group member, which it calls the group anniversary target. That is an operational aim, not a legal limit: the statutory deadline remains 12 months from the filing date. EM1514 also notes that a company in a group that is not small is required to tick the box on page 1 of the CT600 saying so.
Worried about an HMRC check? Tax investigation insurance pays your accountant’s fees if HMRC opens an enquiry or compliance check. Solar Protect cover pays up to £100,000 with no excess. It never pays tax, interest or penalties.
From £108.75 a year (£9.06 a month) for individuals, £117.57 for sole traders and £207.50 for companies and partnerships, including IPT and the £20 admin fee.
See my price in 2 questions or call 01795 841 310.
★★★★★ Rated 4.9 out of 5 on Trustpilot from over 160 reviews
Which groups count as small?
Paragraph 24(7) takes “group” and “small group” from sections 474(1) and 383 of the Companies Act 2006. A group means a parent undertaking and its subsidiary undertakings. Under section 1162 an undertaking is a parent of another if, among other tests, it holds a majority of the voting rights, can appoint or remove a majority of the board, or has a right to exercise dominant influence. Because section 1161 defines an undertaking as a body corporate, partnership or unincorporated association carrying on a trade or business, two companies owned directly by the same individual do not form a group in this sense, even though they may be associated companies for corporation tax rates.
Under section 383 a group meets the qualifying conditions in a year if it satisfies two or more of these:
| Test | Financial years beginning on or after 6 April 2025 | Earlier financial years |
|---|---|---|
| Aggregate turnover | Not more than £15 million net (£18 million gross) | Not more than £10.2 million net (£12.2 million gross) |
| Aggregate balance sheet total | Not more than £7.5 million net (£9 million gross) | Not more than £5.1 million net (£6.1 million gross) |
| Aggregate number of employees | Not more than 50 | Not more than 50 |
“Net” means after eliminating intra group transactions and “gross” means before, and a group may use either. After the parent’s first financial year, section 383(3) means a group only changes status if it meets, or fails, the conditions in two consecutive financial years. EM1513 still quotes the earlier thresholds, so check the legislation for the year concerned.
EM1512 tells officers to identify the whole group first, including an overseas ultimate parent or intermediate parent. A company that sits in a small sub group is still a member of a group that is not small if the wider group headed by its ultimate parent is not small. EM1513 says HMRC will normally look at the parent’s consolidated accounts to see whether the conditions are met.
How does the filing date move the window?
Because the group window is tied to the filing date, anything that changes the filing date changes the window. Under paragraph 14 the filing date is the last day of whichever of these ends last: 12 months from the end of the return period; 12 months from the end of the period of account if that is not longer than 18 months; 30 months from the start of a period of account longer than 18 months; or three months from the date the notice requiring the return was served.
So where HMRC serves a notice to deliver a company tax return late, the filing date moves and, for a group company that is not small, so does the end of the enquiry window. EM1511 gives an example where a late notice moved the filing date to 6 April 2020 and the group company’s window to 6 April 2021, while the window for a standalone company filing on the same day was unchanged.
What happens if a group company files late?
Paragraph 24(6) only modifies the 12 month period in paragraph 24(2), which applies to returns delivered on or before the filing date. A late return falls under paragraph 24(3) instead, so the group rule drops away and the window runs to the quarter day after the first anniversary of actual delivery. EM1511 illustrates this: a return with a filing date of 31 December 2019 delivered on 8 June 2020 can be enquired into up to 31 July 2021. The result is that a late return always leaves HMRC more time than an on time one, for group and standalone companies alike, on top of any late filing penalties.
What about amended returns?
A company can amend its return up to 12 months after the filing date (paragraph 15(4)). An amendment gives HMRC a fresh window to the quarter day after the first anniversary of the amendment, for every company. EM1510 adds that if the amendment is made while the window for the original return is still open, an enquiry then opened covers the whole return, not just the amendment. Paragraph 24(5) allows only one notice of enquiry per return, except for a further notice given because of an amendment.
How does this work in practice?
Illustration only. Each company has a year ended 31 March 2026 and a filing date of 31 March 2027.
| Situation | Delivered or amended | Enquiry window closes |
|---|---|---|
| Standalone company, or company in a small group, filed on time | 15 September 2026 | 15 September 2027 |
| Company in a group that is not small, filed on time | 15 September 2026 | 31 March 2028 |
| Company in a group that is not small, filed late | 20 May 2027 | 31 July 2028 |
| Company in a group that is not small, return amended | 10 February 2028 | 30 April 2029, for the amendment |
In the last row the amendment was made while the original window was still open, so an enquiry opened before 31 March 2028 would cover the whole return.
What mistakes come up?
- Assuming an early filed group return is safe after 12 months. For a group that is not small, the clock starts at the filing date.
- Testing only the sub group. EM1512 looks to the widest group, including overseas parents.
- Using the wrong group test. The Companies Act group and its size limits apply here, not the associated company or group relief definitions.
- Using the pre April 2025 thresholds for a later year, or forgetting the two consecutive years rule.
- Forgetting that a closed window does not end exposure. HMRC can still use a discovery assessment if the conditions are met.
If HMRC opens a check into your return, tax investigation insurance pays your accountant’s fees. Solar Protect cover pays up to £100,000 with no excess; it never pays tax, interest or penalties. Read how our cover works or get a quote.
Related Accountapedia entries
- Group Relief for Corporation Tax
- Group payment arrangements for corporation tax
- How long HMRC has to enquire into an SDLT return
- How long HMRC has to open an enquiry into a return
- Corporation tax for property investment companies
Sources
- legislation.gov.uk: Act 1998 c. 36, schedule 18
- GOV.UK: Manual page EM1510
- GOV.UK: Manual page EM1514
- legislation.gov.uk: Act 2006 c. 46, section 474
- legislation.gov.uk: Act 2006 c. 46, section 1161
- legislation.gov.uk: Act 2006 c. 46, section 1162
- legislation.gov.uk: Act 2006 c. 46, section 383
- legislation.gov.uk: SI 2024/1303, regulation 2
- legislation.gov.uk: Act 2006 c. 46, section 383
- GOV.UK: Manual page EM1513
Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 24 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.