Abbey National and its agents Eversheds told me that that I was 'required to' fill in its I&E form, which of course demanded personal data about my new partner and my two small children. I did two three things: (1) complained to the Information Commissioner; (2) asked my MP for help; and (3) I went to the press about this unacceptable practice.(posted 8259 days ago)The results? (1) A letter from the IC saying that if the lender had indeed succeeded in getting my new partner's personal details out of me by implying that I was under a duty to do so, then the lender would have been in breach of the Data Protection Act. (That's very much a summary of the letter!)(2) My MP Mike Hancock has been excellent and even tabled an Early Day Motion about lenders' failure to substantiate these claims, in particular Abbey National. (3) The Mail on Sunday published an article last year about the invasion of privacy that these I&E forms represent.
I can't advise you what to do, but that's what I did.
I should also add that you should make your own separate formal complaint to the lender, and then take it to the Ombudsman. I would.