Double Taxation applications and claims: Repayment claims from non-residents: Combined applications and claims for repayment
A combined application and repayment claim does involve a claim (the repayment claim element) subject to the self assessment (SA) rules. So if you receive a form containing both an application for relief at source and a repayment claim you must apply the SA procedures.
For the avoidance of doubt that means you must follow the SA rules and procedures for opening an enquiry as set out in INTM331200. Asking the claimant or tax adviser for information about the application for relief at source could be taken to be asking for information relating to the claim without opening an enquiry.