Oh dear what have I done?
I ran the year end tool to 05/04/2015 and after doing so I noticed that the chart of nominal accounts had set itself to 01/01/1900 - 05/04/2016. So I changed it to 06/04/15 - 05/04/16 and pressed update.
Now when I look at the accounting period 06/04/2014 - 05/04/2015 the nominal accounts information has been wiped apart from the “assets and liabilities” and “capital and reserves” sections