Extract . . .
"People hit with an unexpected tax demand may be able to refuse to pay as HM Revenue & Customs could have exceeded its own time limits in which to ask for the money, experts have said."
Link
http://www.telegraph.co.uk/finance/personalfinance/consumertips/tax/7984853/PAYE-tax-error-HMRC-may-be-too-late-to-demand-money-back.html