From the limited amount I have read about these schemes, they appear generally thought to be considered not a good idea in most people's cases.
I believe there are two types of scheme. Someone I know entered into what I think is called a drawdown scheme where money is drawn down as and when and in the amounts needed. Therefore interest only accrues on what has been drawn down. The other scheme, I think, is where a large amount of money is made available all at once and therefore interest accrues on that larger amount right from the start. As has already been mentioned, the interest owing soon mounts up.
Personally speaking, if it were possible, I would downsize or rent out a room.