couldn't you remortgage on a buy to let on your own property I think they let you borrow up to 80%.
We have just done this as our buyers pulled out and left us with no time to find another.
We had the mortgage in place within 10 days and had 5 viewing to rent it on Monday and with the amount of money we have coming in from rent I dont intend to sell untill the exchange rate goes above $1.80.
To be honest It may turn out to be a blessing that they pulled out, we will have to wait and see.
Good luck either way.