Over 685,000 Self Assessment taxpayers who accessed their 2015/16 SA Return via their Personal Tax Account between August 2016 and March 2017 had their returns pre-populated. The worry was whether pre-population would lead to less accurate tax returns, as taxpayers simply assumed online figures were correct.
HMRC looked at a sample to see how they reacted. 17% overwrote a pre-populated income figure and 15% overwrote an employment benefit figure. Comparing pre-population to those without showed improved accuracy of income reporting, with some over-writing with higher amounts and some with lower amounts. However, it cost money, due to improved accuracy, since taxpayers reducing overpayments outweighed the reduction in small underpayments. The full results are in a letter from HMRC chief executive Jon Thompson to the Public Accounts Committee