Certainly you should ask Skipton to prove that it valued and marketed the property properly and sold it at best value. Skipton lost an important Court of Appeal case last year (Skipton Building Society v Stott 2000 CA, I believe)on these issues.(posted 8305 days ago)People who fill in I&E forms because they think they have to do so should not worry too much about having 'admitted liability', IMHO. You did not give informed consent for the lender to pry into your affairs, because the claim was not substantiated. In fact, there may well be data protection issues here, if the lender gave the impression that you had some sort of legal obligation to give up your personal data and/or that of a partner/child. Anyhow, is is legally possible to 'resile' (withdraw)'liability', I understand. There is some case law on this.
Keep calm, and start asking the lender to prove its claim. Be polite but firm, keep your nerve, and come back to this board as often as you need. Definitely ask about the vaulation, marketing and sale price. Wsa it marketed at all? Wsa it flagged in some way as a 'repo'? If so, why? Etc etc.