HMRC has the power to investigate your tax affairs going back up to 20 years in cases of serious tax evasion or fraud. However, for most cases, the time limit is much shorter.
Generally, HMRC can investigate your tax affairs for up to 4 years after the end of the tax year in question. This means that if you filed your tax return for the 2019/20 tax year on time, HMRC has until April 2024 to start an investigation.
It’s important to note that this time limit can be extended in certain circumstances, such as if you have deliberately concealed information or if HMRC suspects criminal activity.