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HMRC letter codes · One-to-many letters

CompC1aESSMMLetter about undeclared sales and a chance to make a disclosure, version a

Published by its source on 26 April 2023. A date in the letter that has passed stays passed: what a passed date means.

Last reviewed 14 October 2026 · How Tax Letters checks its facts

In short

HMRC's letter CompC1aESSMM is headed “Tell us about any undeclared sales”. In this version the letter says that if the reader does not make a disclosure by the deadline, HMRC will contact them again.

“CompC1aESSMM … Tell us about any undeclared sales … If you do not make a disclosure by the deadline, we will contact you again.”

ICAEW: HMRC letter CompC1aESSMM, as published with its tax news item · checked 14 October 2026

Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CompC1aESSMM. Each fact has its source and the day it was checked beside it.

What it is

ICAEW lists HMRC's letter CompC1aESSMM as the electronic sales suppression letter April 2023 version a, and said two different versions of the letter were used to determine the best approach.

“Two different versions of the letter will be used to determine the best approach going forward. … HMRC electronic sales suppression letter April 2023 version a”

ICAEW: HMRC’s letters to businesses regarding electronic sales suppression · checked 14 October 2026

When HMRC sends it

HMRC's letter CompC1aESSMM says HMRC has information that suggests the reader may have misused their till system to reduce their tax bill, which means they may owe tax.

“CompC1aESSMM … We have information that suggests you may have misused your till system to reduce your tax bill. This means you may owe tax.”

ICAEW: HMRC letter CompC1aESSMM, as published with its tax news item · checked 14 October 2026

ICAEW said, in the news item with HMRC's letter CompC1aESSMM, that businesses who might not have paid the correct income tax, corporation tax or VAT owing to misuse of their till systems were receiving letters from HMRC.

“Businesses who might not have paid the correct income tax, corporation tax or VAT owing to misuse of their till systems are receiving letters from HMRC.”

ICAEW: HMRC’s letters to businesses regarding electronic sales suppression · checked 14 October 2026

What it asks

HMRC's letter CompC1aESSMM says HMRC is giving the reader the chance to tell it about undeclared sales by making a disclosure.

“CompC1aESSMM … We are giving you the chance to tell us about your undeclared sales by making a disclosure.”

ICAEW: HMRC letter CompC1aESSMM, as published with its tax news item · checked 14 October 2026

Free help and HMRC contacts

HMRC's letter CompC1aESSMM points to GOV.UK, search “make a disclosure about misusing your till system”.

“CompC1aESSMM … Go to GOV.UK and search ‘make a disclosure about misusing your till system’.”

ICAEW: HMRC letter CompC1aESSMM, as published with its tax news item · checked 14 October 2026

HMRC's letter CompC1aESSMM says anyone whose health or personal circumstances make it difficult to deal with HMRC can tell HMRC, and points to GOV.UK, search “get help from HMRC if you need extra support”.

“CompC1aESSMM … If you have any health or personal circumstances that may make it difficult for you to deal with us, please tell us. … For more information, go to GOV.UK and search ‘get help from HMRC if you need extra support’.”

ICAEW: HMRC letter CompC1aESSMM, as published with its tax news item · checked 14 October 2026

Free help first

These routes are described by GOV.UK, TaxAid and Citizens Advice themselves.

  • HMRC's extra supportHMRC offers extra support if your health condition or personal circumstances make it difficult to contact HMRC, for example a mental health condition, financial hardship or being treated in hospital.
  • Someone to deal with HMRC for youYou can authorise a friend, relative or voluntary organisation to talk to HMRC for you and help you fill in forms.
  • TaxAidTaxAid helps people with tax problems who cannot pay for advice. Tax Help for Older People merged with TaxAid in July 2025.
  • Citizens AdviceCitizens Advice gives confidential advice online, over the phone and in person, for free.