Hi. HMRC are now proactively putting their hands in taxpayers pockets and helping themeselves without asking us - see vultures. In this client's case (employment income with car benefit and some rental income), the HMRC system didnt pick up (!) the car BIK on the P11d and therefore the wrong tax code operated in 2016/17. However, in 2017/18 HMRC decided to increase the cash equivalent of the BIK by double (£15k*2) to collect the underepayment in 2016/17 via the tax code for 2017/18! The problem is the employee will file a tax return for 2016/17 in which the benefit will be declared and tax will be paid. That means paying the tax on the BIK twice (once via the 2016/17 tax return and twice via the 2017/18 tax code), which of course wouldnt pose a problem if it wasnt for a £6k bill cash flow disadvantage for the poor taxpayer. I have looked up the IYA HMRC manual https://www.gov.uk/hmrc-internal-manuals/paye-manual/paye11100 but no explanation how get round this "small" problem! i should be grateful if a member could help with this - many thanks.