In most cases, your solicitors will also be acting for the lender. If not, they will istruct their own solicitors (who you will have to pay for). They will only release the deeds to your solicitor to hand over on the basis that they will be returned or the loan will be paid off. It is probably registered land so the land registry will not issue a land certificate unless the charge is removed by the lender as the loan is paid off. Simply, in practical terms, you must pay the loan off or your purchasers will not go through with the deal - their solicitors will make sure of that.