CompC2MRRMMLetter asking a company to check it claimed the right Marginal Relief

HMRC's letter CompC2MRRMM says HMRC has information that shows the company has associated companies but has not declared them when claiming Marginal Relief, which means it may have claimed the wrong amount.

“CompC2MRRMM … We have information that shows your company has associated companies, but hasn’t declared them when claiming Marginal Relief on a Company Tax Return. This means your company may have claimed the wrong amount of Marginal Relief.”

CIOT: copy of HMRC letter CompC2MRRMM, published on its page · checked 14 October 2026

CIOT said, on its page for HMRC's letter CompC2MRRMM, that HMRC had started a One to Many letter campaign directed at companies it had identified as having potentially not declared associated companies in their Corporation Tax returns and thus potentially having claimed higher marginal rate relief than they were entitled to.

“HMRC have advised us that they have recently commenced a One to Many letter campaign directed at companies that HMRC have identified as having potentially not declared associated companies in their Corporation Tax returns and thus having potentially claimed higher marginal rate relief than they are entitled to.”

CIOT: HMRC One to Many letter - Marginal Rate Relief · checked 14 October 2026

CIOT lists HMRC's letter CompC2MRRMM as “Letter 2 - Please check you’ve paid the right amount of Corporation Tax”, and said two letters were being used to test different framing and tone.

“Two letters are being used. … Letter 2 - Please check you’ve paid the right amount of Corporation Tax”

CIOT: HMRC One to Many letter - Marginal Rate Relief · checked 14 October 2026

HMRC's letter CompC2MRRMM asks the reader to check the Company Tax Return for the accounting period that includes 1 April 2023, and all later returns.

“CompC2MRRMM … Check your Company Tax Return for the accounting period that includes 1 April 2023, and all later returns.”

CIOT: copy of HMRC letter CompC2MRRMM, published on its page · checked 14 October 2026

HMRC's letter CompC2MRRMM points to GOV.UK, search “Company Tax”, then “Making Changes”, to amend a return.

“CompC2MRRMM … To do this, go to GOV.UK, search ‘Company Tax’ and choose ‘Making Changes’.”

CIOT: copy of HMRC letter CompC2MRRMM, published on its page · checked 14 October 2026

HMRC's letter CompC2MRRMM points to GOV.UK, search “HMRC extra support”, for a reader whose health or personal circumstances make it difficult to deal with HMRC.

“CompC2MRRMM … If you have any health or personal circumstances that make it difficult for you to deal with us, please tell us. … For more information, go to GOV.UK and search ‘HMRC extra support’.”

CIOT: copy of HMRC letter CompC2MRRMM, published on its page · checked 14 October 2026