If the contract is subject to mortage approval, and you don't have mortgage approval - end of contract, end of story.
If you have mortgage approval but the bank won't now release the money, it's the same story. How can you expect to fulfill the contract if a key element is not in place?
If on the other hand you have mortgage approval but now regret ever signing the contract and don't want to complete it, that's your problem and you should get a solicitor.
If the developer is able to enforce a judgement against you and you refuse or are unable to pay, he might be able to bankrupt you. In which case, the transfer you have just done would be voided anyway.
You could get the bank to give you a bank draft and "lose it" until the fuss dies down. Even a bankruptcy only lasts 12 years... (rofl).