Question: hmrc have made a mistake?
Answer: You can ask HM Revenue and Customs ( HMRC ) to cancel tax you owe ('arrears') if you think they've made a mistake because they didn't act on information they had. This guide is also available in Welsh (Cymraeg). You can do this by asking for an 'extra-statutory concession' ('ESC A19') if you owe: ... Capital Gains Tax.