Halifax have just sent me a letter saying they are giving me a goodwill payment (worth several hundred pounds) as the wording on my original agreement was unclear. I don't know how I missed this (I googled it and theirs loads of info on it!) but just thought it was worth mentioning that you may be eligable if you took your mortgage out with them between 09/04 and 09/07.
They have offered to credit my mortgage, but I rang them and they are also offering to send a cheque instead.