Most brown envelopes from HMRC are routine: a tax code notice, a P800, a Simple Assessment bill or a reminder to file. Open it the day it arrives, check it is genuine, find the deadline, and get advice before you answer any questions HMRC asks.
Don't leave a brown envelope from HMRC unopened on the side.
Most of them are routine. But some carry deadlines that run from the date printed on the letter, not the day you get round to opening it.
What is usually inside?
These are the letters business owners and directors get most often:
| Letter | What it means | What to do |
|---|---|---|
| Tax code notice | The code your employer or pension provider will use to take tax from your pay | Check the allowances and any benefits listed are right |
| P800 tax calculation | You paid too much or too little tax through PAYE last tax year | Check the figures, then claim the refund or see how the tax will be collected |
| Simple Assessment | A bill for tax HMRC cannot collect through your tax code | Check it, and contact HMRC within 60 days if anything is wrong |
| Notice to file a Self Assessment return | HMRC expects a tax return from you | File by the deadline, or tell HMRC if you think you don't need to |
| Notice to deliver a Company Tax Return (CT603) | Your company has to file a Company Tax Return | Pass it to your accountant |
| Compliance check letter | HMRC wants to check a return, your accounts or your records | Get advice before you reply |
A P60 doesn't come from HMRC. Your employer or pension provider sends it after the tax year ends.
Is the letter genuine?
Scammers copy HMRC letters, emails, texts and calls. Before you ring a number or pay anything:
- Don't use the phone number or link in the message. Find HMRC's contact details on gov.uk yourself, or sign in to your HMRC online account and check what's on record
- HMRC doesn't send tax rebate notifications or ask for personal or payment details by text
- Genuine HMRC emails about rebates or payment details come from addresses ending in hmrc.gov.uk
- Forward suspicious emails to phishing@hmrc.gov.uk and suspicious texts to 60599
What should you do when it arrives?
- Open it the day it arrives and note the date on the letter
- Find the deadline: a reply date, a payment date, or the 60 days you have to query a Simple Assessment
- Check the figures against your own records, such as your salary, dividends, benefits and tax code
- If something is wrong, tell HMRC. If you can't pay, ask about a payment plan before the due date
- If the letter asks you questions, speak to an accountant before you answer
What if you owe tax?
Tax paid late carries interest at the Bank of England base rate plus 4%, the margin HMRC has charged since 6 April 2025.
If you can't pay in full, HMRC may agree a payment plan. It checks the plan is affordable, and it expects you to use savings and assets to reduce the debt first.
If you're due a refund on a P800, it's paid within 5 working days when you claim online. Otherwise a cheque is posted to you.
What if it's a compliance check?
This is the letter to take seriously. HMRC writes to say what it wants to check, whether that's a Self Assessment return, a Company Tax Return, your accounts or your payroll records.
For a personal tax return filed on time, HMRC has 12 months from the date it received the return to open an enquiry. Outside that window it can still assess tax it finds missing: normally up to 4 years back, 6 years if the mistake was careless, and 20 years if it was deliberate.
Answer exactly what HMRC has asked, by the deadline, and nothing more. How to do that is covered in how should you respond to an HMRC enquiry letter.
If you have an accountant, HMRC will contact them instead. If a letter reaches you directly anyway, send it on the same day.
Where does this come from?
Letter types and deadlines are from HMRC's guides to tax overpayments and underpayments, Simple Assessment and tax compliance checks. Scam reporting is in report HMRC phishing emails, texts and phone call scams. Payment plans are in if you cannot pay your tax bill on time, and the interest rate is in HMRC interest rates for late and early payments. The time limits are in HMRC's Enquiry Manual and Compliance Handbook.
What a letter means for you depends on your own tax affairs, so this is general information rather than advice on your position. If a brown envelope has arrived and you're not sure what it means, talk to us.
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Book a discovery callCommon questions
Don't use the contact details in the letter itself. Check them against HMRC's contact details on gov.uk, or sign in to your HMRC online account. HMRC doesn't send rebate notifications or ask for personal or payment details by text. Forward suspicious emails to phishing@hmrc.gov.uk and texts to 60599. See [report HMRC phishing emails, texts and phone call scams](https://www.gov.uk/government/organisations/hm-revenue-customs/contact/reporting-fraudulent-emails).
A P800 is a tax calculation telling you that you paid too much or too little tax through PAYE in the last tax year. HMRC sends them between June and March of the following tax year, and only to people who are employed or get a pension. See [tax overpayments and underpayments](https://www.gov.uk/tax-overpayments-and-underpayments).
You must contact HMRC within 60 days if you think any information in your Simple Assessment is wrong. See [Simple Assessment](https://www.gov.uk/simple-assessment).
For a personal return filed on time, HMRC can open an enquiry within 12 months of receiving it. Separately, it can assess missing tax normally up to 4 years after the end of the tax year, 6 years if the error was careless and 20 years if it was deliberate. See HMRC's [Enquiry Manual](https://www.gov.uk/hmrc-internal-manuals/enquiry-manual/em1506) and [Compliance Handbook](https://www.gov.uk/hmrc-internal-manuals/compliance-handbook/ch53100).
Deadlines still run. Tax paid late carries interest, and you may have to pay a penalty if you don't send information HMRC asks for in an information notice, unless you have a reasonable excuse. See [tax compliance checks](https://www.gov.uk/tax-compliance-checks).
Simon Jacobs is a Chartered Tax Adviser (CTA · ACA) and PwC trained, founder of SRJ International. He advises UK business owners on tax, profit extraction and exit. Read his full profile →
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