Try a local Upvc shop for advice they may put you onto a shop that sells plastic strips to overlay the damaged area and advize what type of adhesive you will need. Then again they may try selling you a new door. You could try yellow pages for a plastics supplyer who is local. Sorry can't be more useful.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix windows and doors.