RM5108 | Claims: You think the claimant may want to claim
From HM Revenue & Customs · Repayment Claims Manual
Before a year goes out of date you may receive a general enquiry about a claim, or you may be asked for a claim form.
Although a specific claim has not been made you may feel a claimant wants to make one. If there is sufficient time you should warn the claimant about the time limit. If it is too late to expect the claimant to make a formal claim in time
accept the letter as an intention to claim
send the warning set out in RM5104.