Double Taxation applications and claims: Repayment claims from non-residents: Amendments of claims - corrections
You can correct any obvious errors or mistakes in a claim without opening an enquiry. You have 9 months to do this from the date HMRC received the claim (not from the date the claim reached you).
Examples of obvious mistakes or error include arithmetical mistakes, transposing figures, entering the net income instead of the gross amount and including tax other than UK income tax.
A claimant may amend his claim by notice (to an officer of Revenue & Customs) at any time up to 12 months from the date he made the claim.
For full guidance on how to correct a claim see INTM331100.