by Asim Abbas
12 November 2026 
HMRC has contacted me about undeclared income: what should I do now?
HMRC has contacted me about undeclared income: what should I do now?
A letter from HMRC about income you have not declared is stressful, but ignoring it is the worst thing you can do. Even after HMRC has made contact, a quick and complete disclosure can still reduce the penalty.
- Do not ignore the letter, and do not guess the figures.
- If HMRC has opened an enquiry, tell the officer handling it.
- Early, full disclosure can still reduce the penalty sought.
- A disclosure is unlikely to be accepted through the normal route once an enquiry has opened.
- Get advice before replying, especially if the error may have been deliberate.
HMRC sends different kinds of letters, from gentle “nudge” letters to formal enquiries. How you respond matters.
This guide explains what to do, based on HMRC’s guide to making a disclosure, updated 15 October 2026.
What kind of letter is it?
- A nudge or campaign letter asking you to check your tax affairs, often using data HMRC holds about rental income, online sales, crypto or overseas accounts
- A request for information about a specific item
- An enquiry or compliance check into a tax return
- A letter offering the Contractual Disclosure Facility, where HMRC suspects deliberate tax loss
Each needs a different response. If you are not sure which you have, send it to us before replying.
If HMRC has already opened an enquiry
According to HMRC’s guide, you should tell the officer conducting the enquiry. Early, full disclosure can still reduce the penalty HMRC seeks. A voluntary disclosure through the normal online route is unlikely to be accepted once an enquiry is already open.
Who to call
- onshore disclosures where HMRC has contacted you: 0300 123 0998 (+44 300 123 0998 from abroad)
- voluntary disclosures where HMRC has not contacted you: 0300 123 1078
- offshore matters: HMRC’s Offshore Disclosure Facility helpline
Estimate your disclosure
Our free HMRC disclosure calculator works out tax, interest to today and penalties for each year, with PDF or CSV download.
What not to do
- do not ignore the deadline in the letter
- do not give HMRC estimated figures without checking them
- do not deny income that HMRC may already have data on
- do not destroy or alter records
If the letter mentions the Contractual Disclosure Facility
This means HMRC suspects deliberate behaviour. You have a limited time to accept or reject the offer, and the decision has serious consequences. Read our guide to the Contractual Disclosure Facility and our guide to HMRC criminal investigations, and get specialist advice immediately.
Fixed-fee accountancy support
Transparent monthly packages for sole traders, landlords and limited companies. Fixed fees agreed upfront, VAT included.
Get a fixed-fee quoteCall 0161 531 4179How we help
We read the letter, explain what HMRC is asking for and why, check your records and prepare a complete and accurate response. Where a disclosure is needed, we calculate the tax, interest and penalty and deal with HMRC on your behalf. See our tax investigation support and our guide to disclosure penalties.
Voluntary disclosure help near you
We help clients make disclosures across the UK, including London, Manchester, Birmingham, Leeds, Liverpool, Bristol, Newcastle, Cardiff and Wales, and in Scotland from Glasgow to Edinburgh. Start with our voluntary tax disclosure service.
What should I do next?
Diary the response date in the letter.
Bank statements, invoices, tenancy or sales records.
A careless answer can raise the penalty.
We will tell you what it means and what to do next.
Frequently Asked Questions
Can I still make a voluntary disclosure after HMRC contacts me?
If HMRC has opened an enquiry, tell the officer handling it. Early, full disclosure can still reduce the penalty, but it will be treated as prompted.
What is a nudge letter?
A letter asking you to check your tax affairs, usually based on data HMRC holds. It is not an enquiry, but it should not be ignored.
What number do I call if HMRC has contacted me?
For onshore disclosures where HMRC has contacted you, 0300 123 0998, or +44 300 123 0998 from abroad.
Will I be prosecuted?
Most cases are dealt with through civil penalties. Serious deliberate cases can lead to a criminal investigation, so get advice early.
Can you deal with HMRC for me?
Yes. With your authorisation we handle all correspondence with HMRC.
Need help with this? Wingate Accountants offers fixed-fee online accountancy support across the UK. Call 0161 531 4179 or request a quote at wingateaccountants.co.uk.
About the Author
Ali Imran
I’m Ali Imran, an accountant at Wingate Accountants. I help sole traders, landlords and directors get their returns filed early and accurately, without the last-minute panic.
