I'm preparing a 2017/18 self assessment tax return. The 2017/18 income does not exceed the basic rate band but there is a significant amount of income at the higher rate in 2016/17.
Do I amend the 2016/17 return or make the entry in the 2017/18 return? There is also guidance that the carry back must be done before the 2017/18 return is submitted. I don't understand why.