I think what is clear here is that the BOI wish to exercise a "lien" over the property which you and your husband bought in order to use that to offset your husband's debts insofar as his "half" of the asset goes.(posted 7493 days ago)This is perfectly legal and they are clearly not going to let you BOTH walk away with the proceeds of your sale when your husband owes other accounts with the same bulding society as this would prejudice their rights to the excess.
You need to take some speedy professional advice over this - if you don't and the BOI take legal proceedings over the house (i.e. to repossess it) you are both likely to lose your home.