HMRC have issued a 'Check of Tax Calculation for the year ended 5 April 2016, 5 April 2017 and 5 April 2018' on the basis that under the automatic exchange of information my client has underdeclared foreign income in 2016/17. Although the letter is out of time for 2016 and 2017 if we do not cooperate, HMRC advise they will assess under the discovery provisions S29 tma 1970. They give a figure of what they belive the correct figure for one particular holding should be for the year ended 5 April 2017. There is no mention of an undepayment for the otehr two years 5 April 2016 and 5 April 2018. So on the face of it, it would appear that it is just one amount that may be incorrect on the 2016/17 tax return. However in the 'schedule of information needed' attached to the back of the letter, they are asking for full breakdown of all income received both in the UK and worldwide for all 3 years. My client is non dom but pays tax on world income and does not claim remittance basis. Can HMRC ask for all this info for all 3 years even though their discovery appears to relate to one source of foreign income in 2016/17? They probably can for 2018 as within the enquiry window but what about the other years? they are basically asking for a breakdown of all figures shown on all tax returns.