Refer Nationwide to the following Court of Appeal Rulings -(posted 8601 days ago)05/01/96 Nat. Prov BS v Lloyd - Mortgage repossession may be deferred as long as necessary if sale to be completed ;
25/01/96 - Nat. Prov. BS v Lloyd - Length of suspesion of possession order to allow sale is a question for each case ; (You don't indicate whether a possession has yet been granted or if you've had any arrears build up;
02/05/96 - Bristol & West v Ellis - Mortgage repossession order to be made if no prospect of sale within 3-5 years; (In your case that's a big 'if' !!)
Finally, subject to how your account has accrued any arrears or spurious charges, see the Sunday Times 08/03/98 in which the Nationwide refunded a customer #26,500 of penalty charges. This article was a follow up to an earleir article I instigated on 22/06/97 principally about the Bradford & Bingley and their concealed 'fines'. (All Bradford & Bingley shortfall victims please note).
If the Nationwide do not have a possession order already, then put them to 'strict proof' of their account and all calculations.
With best wishes. Vic