I can't testify to my statement being 100% true without a lot of tedious searching on the UK FSA/SFA/FCA/whatever they are now's website. But that's what I have a vague recollection of.
It's similar to HMRC's "we can come after you for unpaid tax for 7 years", but you can only go after the HMRC for 5 years for overpaid tax.
The rules are ultimately for the benefit of long term investigations such as the LIBOR rigging, and Guinness trials.
