Just tell them you are withdrawing your offer then. They either want to sell or they don't. They decide. You are the one passing them a large sum of money.We found another house yesterday. All spot on so offered asking price there and then.
The vendors still want to honour a viewing this Saturday
Only reason for "honouring" another viewing is in case the Sat people offer more money which means they'll be open to higher offers at any point ...
Ian