INTM333820 | Double Taxation applications and claims: refusal of relief: What to do if relief is not available - claims
From HM Revenue & Customs · International Manual
If relief is not available on
a claim for repayment of tax, including a payment of tax credit
a claim for personal allowances
a claim for exemption on a PAYE pension
you should follow the guidance about self assessment and how to open an enquiry into a claim at INTM331200.
In these circumstances you must open an enquiry. You cannot simply write to the claimant or agent and say that no relief is due.