HMRC letter codes · One-to-many letters
One-to-many letters, explained by code
Last reviewed 14 October 2026 · How Tax Letters checks its facts
HMRC sends some letters to many people at once, about one subject. These are often called one-to-many letters, and most carry a reference code printed on the letter. A few are known only by the name of the file in which a professional body publishes the letter, and their pages say so. The letters here are the ones professional bodies such as ICAEW, CIOT and LITRG have published. Each code page reports what HMRC, GOV.UK or a recognised body publishes about it, with the source and the day it was checked beside each fact.
Every One-to-many letters code
- NISPAR1MM National Insurance paid over State Pension ageIts own guide on this site
- LCL2REG2MM Class two National Insurance and State PensionIts own guide on this site
- CompC1LPLRMM Letter about income from property lettingsHMRC's letter CompC1LPLRMM is headed “You may need to declare income from property”.
- CompC1LPLR(A)MM Covering letter to agents about property lettings lettersHMRC's letter CompC1LPLR(A)MM is a covering letter that encloses a copy of the letter HMRC sent to the agent's client.
- HEIPO2MM Letter saying a business may need to register for VATHMRC's letter HEIPO2MM is headed “You may need to register for VAT”.
- CI357MM Letter about income from online marketplace salesHMRC's letter CI357MM is headed “Income you have earned from Online Marketplace sales”.
- CompC1OMSCMM Letter about income from online marketplace salesHMRC's letter CompC1OMSCMM is headed “Please tell us about income you’ve earned from online marketplace sales”.
- MM1aHICBCSA Letter asking whether the High Income Child Benefit Charge is dueHMRC's letter MM1aHICBCSA is headed “Check if you need to pay the High Income Child Benefit Charge”.
- HICBCDS1gMM Letter about the High Income Child Benefit Charge and paying through a tax codeHMRC's letter HICBCDS1gMM is headed “Please check if you need to pay the High Income Child Benefit Charge”.
- CompC1ABMM Letter about income from breeding or selling animalsHMRC's letter CompC1ABMM is headed “You may need to declare income from the breeding or sale of animals”.
- CompC2ABMM Letter about income from breeding or selling animals, with a disclosure routeHMRC's letter CompC2ABMM is headed “Tell us about your income from the breeding or sale of animals”.
- CIHT1MM Letter to agents about cryptoassets in Inheritance Tax returnsHMRC's letter CIHT1MM is headed “Please make sure your clients’ Inheritance Tax returns include details of their cryptoassets”.
- CTL24MM Letter about differences in the loss position of Company Tax ReturnsHMRC's letter CTL24MM is headed “Differences in the loss position of Company Tax Returns”.
- WS1NSAMM Letter saying a Self Assessment return may be due, first of threeHMRC's letter WS1NSAMM is headed “Check your income for the tax year 2022 to 2023”.
- WS2NSAMM Letter saying a Self Assessment account is closed and a return may be due, second of threeHMRC's letter WS2NSAMM is headed “Please submit your tax return for the 2022 to 2023 tax year”. This is the version that says HMRC's records show the reader's Self Assessment account is currently closed.
- WS3NSAMM Letter saying a registered taxpayer has not submitted a return, third of threeHMRC's letter WS3NSAMM is headed “Please submit your tax return for the 2022 to 2023 tax year”. This is the version that says HMRC's records show the reader is registered for Self Assessment but has not submitted a tax return for the tax year 6 April 2022 to 5 April 2023.
- PROR2aMM Letter about a provisional Business Asset Roll-over Relief claim, earlier of twoHMRC's letter PROR2aMM is headed “Please check your 2020 to 2021 Business Asset Roll-over Relief claim”.
- PROR2bMM Letter about a provisional Business Asset Roll-over Relief claim, later of twoHMRC's letter PROR2bMM is headed “Please check your 2021 to 2022 Business Asset Roll-over Relief claim”.
- CompC1MPMM Letter asking a consultant to check Self Assessment returns for consultancy feesHMRC's letter CompC1MPMM is headed “Please check your Self Assessment tax returns”.
- CAMM3MM Letter about tax on cryptoasset transactionsHMRC's letter CAMM3MM says HMRC wants to help the reader understand when they need to report cryptoasset transactions and how to update their tax position.
- GHO1MM Letter about a Gift Hold-over Relief claimHMRC's letter GHO1MM is headed “Please check your Gift Hold-over Relief claim”.
- LTATY2MM Letter saying a Business Asset Disposal Relief claim took the reader over the lifetime limitHMRC's letter LTATY2MM is headed “Please check your Business Asset Disposal Relief claim”. This version says HMRC's records show the reader's claim for Business Asset Disposal Relief (BADR) has taken them over the lifetime limit of £1 million.
- LTAAO2(A)MM Letter saying the Business Asset Disposal Relief lifetime limit was already reachedHMRC's letter LTAAO2(A)MM is headed “Please check your Business Asset Disposal Relief claim”. This version says HMRC's records show the reader had exceeded the lifetime limit of £1 million before submitting their latest Self Assessment return.
- AIA3MM Letter about Annual Investment Allowance claims and groups of companiesHMRC's letter AIA3MM is headed “Annual Investment Allowance claims and groups of companies”.
- PF1MM Letter inviting a call before a Self Assessment return is sentHMRC's letter PF1MM is headed “Invitation to a call before sending your Self Assessment tax return”.
- IRInd1MM Letter asking a reader to check an incorporation relief claimHMRC's letter IRInd1MM is headed “Check your incorporation relief claim is correct”.
- CompC11aESSMM Letter about sales that were not declared, with a final opportunity to make a disclosureHMRC's letter CompC11aESSMM is headed “Please tell us now about sales you haven’t declared”. In this version the letter's example of a penalty uses £10,000 of tax.
- CompC11bESSMM Letter about sales that were not declared, with a final opportunity to make a disclosureHMRC's letter CompC11bESSMM is headed “Please tell us now about sales you haven’t declared”. In this version the letter's example of a penalty uses £50,000 of tax.
- CompC1MRRMM Letter asking a company to check it paid the right amount of Corporation TaxHMRC's letter CompC1MRRMM is headed “Check you’ve paid the right amount of Corporation Tax”.
- CompC2MRRMM Letter asking a company to check it claimed the right Marginal ReliefHMRC's letter CompC2MRRMM is headed “Please check you’ve paid the right amount of Corporation Tax”.
- CompC1CRYPTOMM Letter about Capital Gains Tax on cryptoassetsHMRC's letter CompC1CRYPTOMM is headed “Capital Gains Tax on Cryptoassets”. In this version the letter says HMRC has also sent a copy of it to the reader's agent.
- CompC2CRYPTOMM Letter about Capital Gains Tax on cryptoassetsHMRC's letter CompC2CRYPTOMM is headed “Capital Gains Tax on Cryptoassets”. In this version the letter says a reader who has an agent might want to show them the letter.
- CompC1IDMM Letter about distribution or dividend income that may need declaringHMRC's letter CompC1IDMM is headed “You may need to declare distribution or dividend income”.
- CPCE2024008MM Letter to charities about aggregated Gift Aid donationsHMRC's letter CPCE2024008MM is headed “Getting your aggregated donations right”.
- OTM000778 Letter asking a reader to update a Self Assessment return with final figuresOTM000778 is the name LITRG gives to the files of two example HMRC letters on its page, one about provisional figures and one about rounded figures. The number is not printed in either letter. The provisional figures letter is headed “Please update your Self Assessment tax return with final figures”, and this published copy has a placeholder in square brackets where the date to act by belongs.
- OTM000648 Letter about income from online marketplace salesOTM000648 is the name LITRG gives to the file of this HMRC letter. The number is not printed in the letter text. The letter is headed “Please tell us about income you’ve earned from online marketplace sales”, and this published copy has placeholders in square brackets where the dates belong.
- OTM000559 Letter about income from delivery workOTM000559 is the name of the file in which CIOT publishes this HMRC letter. The number is not printed in the letter text. The letter is headed “Declaring your income”.
- OTM000574 Letter to agents about provisional figures in clients’ returnsOTM000574 is the name of the file in which CIOT publishes this HMRC letter to agents. The number is not printed in the letter text. The letter is headed “Please amend the provisional figures in your clients’ Self Assessment tax returns”, and this published copy has a placeholder in square brackets where the date to act by belongs.
- OTM000568 Letter to agents about possible errors in clients’ Self Assessment returnsOTM000568 is the name of the file in which CIOT publishes this HMRC letter to agents. The number is not printed in the letter text. The letter is headed “Please check your clients’ Self-Assessment Tax Returns for potential errors for year ended 5 April 2023”, and this published copy has a placeholder where the case reference belongs.
- R&D2MM Letter asking a company to check its Research and Development tax relief claimHMRC's letter R&D2MM is headed “Check your claim for Research and Development tax relief”.
- CompC1aESSMM Letter about undeclared sales and a chance to make a disclosure, version aHMRC'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.
- CompC1bESSMM Letter about undeclared sales and a chance to make a disclosure, version bHMRC's letter CompC1bESSMM is headed “Tell us about any undeclared sales”. In this version the letter says that making a disclosure will reduce the amount of penalties the reader receives.
Information, not advice: these pages report what HMRC and GOV.UK say about each code. Your own letter comes first.
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Other series
- Self Assessment (SA)SA1, SA401, SA250, SA316, SA100 and more
- Corporation Tax (CT)CT600, CT603, CT41G, CT41G (Clubs), CT208 and more
- VATVAT1, VAT1A, VAT1B, VAT2, VAT7 and more
- National Insurance (CA)CA5603, CA5403, CA2490, CA4361, CA72A and more
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- Debt and payment letters (IDMS)IDMS99, IDMS99P, OCA43
- Compliance check factsheets (CC/FS)The factsheets HMRC's compliance letters name.
- Every HMRC letter codeAll the series on one page.
- ICAEW: HMRC letter CompC1LPLRMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC nudges taxpayers to declare property income and gains (checked 14 Oct 2026)
- ICAEW: HMRC letter CompC1LPLR(A)MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC letter HEIPO2MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC reminds businesses to register for VAT (checked 14 Oct 2026)
- ICAEW: HMRC letter CI357MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC campaign targets income from online marketplaces and digital content (checked 14 Oct 2026)
- ICAEW: HMRC letter CompC1OMSCMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: Online marketplace sellers may have tax to pay (checked 14 Oct 2026)
- ICAEW: HMRC letter MM1aHICBCSA, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: Taxpayers should check HICBC for 2022/23 (checked 14 Oct 2026)
- ICAEW: HMRC letter HICBCDS1gMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: New process for paying the High Income Child Benefit Charge (checked 14 Oct 2026)
- ICAEW: HMRC letter CompC1ABMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: Animal breeders in HMRC’s sights (checked 14 Oct 2026)
- ICAEW: HMRC letter CompC2ABMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC letter CIHT1MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: Agents may be overlooking IHT on cryptoassets (checked 14 Oct 2026)
- ICAEW: HMRC letter CTL24MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: CT600 loss figures may be incorrect (checked 14 Oct 2026)
- ICAEW: HMRC letter WS1NSAMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: Wealthy taxpayers asked to check if tax return required (checked 14 Oct 2026)
- ICAEW: HMRC letter WS2NSAMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC letter WS3NSAMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC letter PROR2aMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC reminds taxpayers about roll-over relief claims (checked 14 Oct 2026)
- ICAEW: HMRC letter PROR2bMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC letter CompC1MPMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: Tax news in brief 30 September 2026 (checked 14 Oct 2026)
- ICAEW: HMRC letter CAMM3MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC targets tax liabilities from cryptoassets (checked 14 Oct 2026)
- CIOT: copy of HMRC letter GHO1MM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC nudge letters for gift holdover relief claims (checked 14 Oct 2026)
- CIOT: copy of HMRC letter LTATY2MM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to many letters and Business Asset Disposal Relief lifetime limit (checked 14 Oct 2026)
- CIOT: copy of HMRC letter LTAAO2(A)MM, published on its page (checked 14 Oct 2026)
- CIOT: copy of HMRC letter AIA3MM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many letter – Annual investment Allowance Group Claims (checked 14 Oct 2026)
- CIOT: copy of HMRC letter PF1MM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many letter – invitation to a discussion with Customer Compliance Managers prior to tax return submission (checked 14 Oct 2026)
- CIOT: copy of HMRC letter IRInd1MM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many Letter – Capital Gains Tax Incorporation Relief – Property Businesses (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CompC11aESSMM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many letter – Electronic Sales Suppression (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CompC11bESSMM, published on its page (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CompC1MRRMM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many letter - Marginal Rate Relief (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CompC2MRRMM, published on its page (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CompC1CRYPTOMM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC’s One to Many letter Cryptoassets project (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CompC2CRYPTOMM, published on its page (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CompC1IDMM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many letter – Inferred Distributions (checked 14 Oct 2026)
- CIOT: copy of HMRC letter CPCE2024008MM, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many Letter – Gift Aid repayment claims (checked 14 Oct 2026)
- LITRG: copy of HMRC letter file OTM000778, the provisional figures version, published on its page (checked 14 Oct 2026)
- LITRG: copy of HMRC letter file OTM000778, the rounded figures version, published on its page (checked 14 Oct 2026)
- LITRG: HMRC ‘nudge’ letters: what you need to do if you included provisional or round sums in your self assessment tax return for 2024/25 (checked 14 Oct 2026)
- LITRG: copy of HMRC letter file OTM000648, published on its page (checked 14 Oct 2026)
- LITRG: HMRC ‘nudge’ letters: income from online marketplaces up to 5 April 2023 – what you need to do (checked 14 Oct 2026)
- CIOT: copy of HMRC letter file OTM000559, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many letter – Delivery Drivers - Declaration of Income (checked 14 Oct 2026)
- CIOT: copy of HMRC letter file OTM000574, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many Agent Letter – Provisional figures in clients’ 2022/23 Self Assessment tax returns (checked 14 Oct 2026)
- CIOT: copy of HMRC letter file OTM 000568, published on its page (checked 14 Oct 2026)
- CIOT: HMRC One to Many Agent Letter – Discrepancies in Clients’ Self Assessment Tax Returns for the year ended 5 April 2023 (checked 14 Oct 2026)
- ICAEW: HMRC letter R&D2MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: Tax news in brief 22 February 2023 (checked 14 Oct 2026)
- ICAEW: HMRC letter CompC1aESSMM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC’s letters to businesses regarding electronic sales suppression (checked 14 Oct 2026)
- ICAEW: HMRC letter CompC1bESSMM, as published with its tax news item (checked 14 Oct 2026)
- GOV.UK: Get help from HMRC if you need extra support (checked 7 Oct 2026)
- GOV.UK: Appoint someone to deal with HMRC on your behalf (checked 7 Oct 2026)
- TaxAid: About us (checked 8 Oct 2026)
- Citizens Advice: About us (checked 7 Oct 2026)