Hold your horses there folks- I think we're jumping the gun a little bit. We're all forgetting that section 3(3) of the 1976 Act says:
"No conveyance shall be void... if it is made to a purchaser for full value"
This exception essentially applies to a bona fide purchaser for value. The definition of purchaser includes mortgagee (bank) and the definition of conveyance includes mortgage. So unless the purchaser (in this case the bank who lent the money) had notice from their own personal knowledge of the fact that borrower was married and that it was in fact their family home, or if that fact would have come to their knowledge if such enquiries and inspections had been made or reasonably ought to have been made then the general rule that the conveyance is void does not apply.
Therefore where, as it appears in this case, that a person deliberately concealed the fact that the property was the family home and that they were married and the bank and/or their agents having made due enquiries do not discover that fact then the non owning spouse is precluded from relying on the general rule that the transaction is void. Accordingly, the issue that this whole thing turns on is whether the bank had actual or constructive notice of these facts and as the borrower/owning spouse would have in the mortgage process had to swear a statutory declaration that the property was not a family home and probably also that they were not married, it is perhaps likely or arguable that these enquiries are about as far as the bank could go or reasonably expected to go in enquiring/ establishing the facts. Thus they probably did not have notice for the purposes of the Act and if this is so, then the mortgage will still be valid and the non-owning spouse will have no protection under the FHPA 1976.
In any event, even if this was not the case and the non-owning spouse was protected under the Act, as another poster has correctly pointed out, the bank would have recourse to normal debt collection court procedures culminating in a well-charging order and an order of possession of the property. Albeit this would be a longer way of repossessing the property it would nonetheless be the banks strategy and ultimately have the same end result, with enormous additional legal cost implications which of course would be borne by the borrower. There are several ways to skin a cat as they say.
So I wouldn't be cracking open the champagne just yet on account of pulling a fast one on the bank!