Cheers Chris for info.
Since my earlier post, I've had a mooch around money saving expert web site and theres a link there directly to the Halifax's page for reclaiming. So sod it, I've downloaded the form and giving it ago.
I took out a mortgage 16 years ago and had PPI. I then changed to a differenct company 5 years ago. Can I still go back and claim against the first mortgage ?