SolvedSIOG9350 | Settlement by agreement: offers: remittance with the offer
From HM Revenue & Customs · Specialist Investigations Operational Guidance
Where a remittance accompanies an offer, its encashment could be interpreted as acceptance of the offer.
The taxpayer or agent should be notified that we are accepting the money as a payment on account and encashment should not be interpreted as acceptance of the offer (see EM1937).
The payment should be sent as a payment on account as per the instructions at SIOG10610.