HM Revenue and Customs' (HMRC) Code of Practice 26 ‘What happens if we’ve paid you too much tax credit?’ explains its approach to tax credits overpayments and the circumstances in which customers may not have to pay them back. It is available at:
http://www.hmrc.gov.uk/leaflets/cop26.pdf
(i) Information about the value of disputed tax credits overpayments written off in each year from 2005-06 to 2008-09 is in the table:
Value of disputed written overpayments written off (£000) 2005-06 180,016 2006-07 9,042 2007-08 7,276 2008-09 28,242
(ii) HMRC does not record the value of overpayments written off as a result of claimant error.