Up to the exchange of contracts nothing is binding. All you have is a Gentleman’s Agreement. The Seller can still sell his house to somebody else but this usually only happens for one of two reasons. He may have received a higher offer from another Buyer, in which case you have been “gazumped”. Alternatively, he may have issued more than one contract and is waiting to see who will exchange first. This is called a Contract Race.
You may also be involved in a chain in which nobody want to exchange contracts on the house they are buying before they exchange on the one that they are selling. Both parties are legally bound only when the contracts are formally exchanged and a Completion Date is agreed. As soon as that happens we will let you know and confirm the completion date.