You could try calling the local dental surgery -- they might be willing to take you. However, it's often hard to get NHS dentistry, and the surgery might only be taking private patients. Make sure you check, because it can be pretty expensive to get work done privately!
Is there a dental hospital in your area? They will usually take patients at short notice. You'll be treated by a (supervised) student, but it's NHS and they can usually see you very soon if you are in pain.