I'm saying that the inheritance part of the situation is dead and gone.
Mr P now owns a property that he wants to take out a mortgage on, in order to develop the site. (It's entirely irrelevant as to how he came by the property. The situation would be the same if he'd owned it for years, rather than having recently inherited it). However he's unwilling, or unable, to take on the mortgage on his own. He therefore propses that Mrs P should take on the mortgage jointly with him but the lender won't allow that to happen unless Mrs P becomes the co-owner of the property. He therefore gifts half of the property to Mrs P. Despite there being no consideration, HMRC still see Mrs P's acquisition as having a chargeable value upon which SDLT must be paid.