Can someone explain the "HMRC has 12 months to launch tax investigation" rule for me?
As I understand it this rule means that if HMRC is going to launch a tax investigation into any one tax year they need to do it within the 12 months of when you filed your tax return (if the return is on-time).
So if you filed your 2016/17 tax return on 9 June 2017, HMRC would have until 9 June 2018 to investigate it. And once that deadline is past can they investigate it any further IF future tax returns don't give them any proof or evidence that something is wrong with that future return (ie: the next return)?
Or I know there is a rule where HMRC can look into your back taxes 4 or 6 years. But can they select any of the previous returns in that 4 or 6 year period even if the 12-month window for that return has already passed if they find nothing wrong with returns after that year?
Or I guess another way I can try to explain what I am trying to ask:
Say the date is 21 February 2018 and I've followed the previous returns on the dates listed below:
2013/14: tax return filed on 15 May 2014
2014/15: tax return filed on 15 June 2015
2015/16: tax return filed on 10 June 2016
2016/17: tax return filed on 15 May 2017
In the return/date examples listed above could on today's date (21 Feb 2018) HMRC choose to randomly investigate my 2015/16 tax return (filed on 10 June 2016) even though the 12-month investigation window would have ended on 10 June 2017? Or if they wanted to investigate that specific return, now that the 12-month window has closed, would they need to prove something wrong with my 2016/17 return (which the 12-month window is still open on) and then say "now we believe because we found X (X being an incorrect number or other problem) we want to see your information for your 2015/16 return?
Basically, I'm wondering if HMRC can pick and choose which return to check in the last 4 or 6 years or if they need to have proof the most recent return is incorrect before they could look into past returns before the most recent?