RM5096 | Claims: Return of claim form is requested
From HM Revenue & Customs · Repayment Claims Manual
If you are asked to return a claim form, what you do depends upon whether or not you have already processed the claim.
If you have already processed the claim do not return the claim form. Tell the claimant politely that it cannot be returned as it is needed for audit purposes.
If the claim is not yet processed
send it back with a covering letter signed by an RE Make sure the letter makes it clear that no repayment will be made until a fresh claim is submitted
clear the registered claim as not pursued (RM5092).