Hi I received a P800 underpayment tax demand for year 2013/14 in November 2014. HMRC has now ruled I should be responsible for this amount and not my employers, HMRC alleged I knowingly worked in 2 jobs at the same time which was not the case. I had in that year worked for 2 employers but never at the same time. One of the employers stated they did not receive my P45, the other had my salary and tronc on 2 payslips that may have resulted in excessive personal allowances and I am not sure if this was the reason HMRC got confused in thinking I had 2 jobs at the same time. Please help.