I'm sure I saw on the Martin Lewis program that you can do the whole process yourself just by getting touch with the ban/building society - thus cutting out the companies.
^ Yes DO NOT let the claims company do it, all you need is to write to the mortgage company yourself and tell them you want to claim. The mortgage company MUST by law inform you of any PPI due and do all the work in tracing it.
PPI companies are legal robbers, all they do is send one letter you can do yourself!
If you have ever taken out, ANY mortgage, loan or credit from anyone, just write to them yourself, using the MSE site if needs be. They, Have to tell you if you had PPI. DIY, everytime.