Definitely do it yourself, I honestly thought it would be difficult or that I would get into some sort of trouble but it was no more painful than printing the letter in Martin Lewis' website that Ilona linked to above and sending it off.
This is something you really shouldn't pay someone to do for you.
Did it myself. Most banks, mortgage lenders have a form you fill in and send with any supporting evidence (original agreement or old correspondence), and a covering letter. Cost me a first class stamp. I have no financial or legal background, but it seemed straightforward. I got 10k back.
thanks - that all sounds great!I'll check out the Money saving expert info. Do you also know if there is any way of tracking down old accounts from years and years ago that we we may have forgotten about?