SDLTM54000 | Overpayment Relief: commencement and time limits
From HM Revenue & Customs · Stamp Duty Land Tax Manual
From 1 April 2011 a person may claim overpayment relief to recover overpaid Stamp Duty Land Tax (SDLT) or to reduce an excessive assessment.
The time limit for a claim to relief is four years after the effective date of the transaction.