My Fathering law many years ago had a discussion with insurers about his building insurance I am not sure if it is still true but the house is insured on market price for the area. He successfully argued that he already owned the land, external landscaping and services where all existing, that their premium was grossly over priced to demolish and build a new house was approx half of the market price they eventually agreed with him. It is fair to say that he did not put it to the test, This was also at a time when insurers where bothered about their customers as well. Not helpful but interesting and true
Keith