Depends entirely on your bank.
The 6 year thing isn't actually true. The FSA only stipulate that banks retain your information for a reasonable length of time, most bans have decided on 6 years and the FSA are happy with that but it's not set in stone.
In fact you'll probably find most banks can go back further than that, anywhere up to 9-10 years isn't uncommon.
However, if you've got any evidence yourself they can use that even if they don't have anything at all.