Try Pickering's in Upper Street Islington as I spoke to my dentist there about the same thing fairly recently. Implants are very expensive as I am sure you know, £3000 and up. My extracted tooth is the lower back tooth, so for now I am learning to live with it. Good luck with it and please let us know how you get on.
I am in the process of having 2 myself: The drilling and inserting of the 2 posts was completed last November, the 2 'teeth' will be made and fitted next month (the wait between the 2 parts of the process is to allow the bone to properly bond with the post and to allow full healing of the gum). I have to say I am very happy with the dentist that is doing mine, actually my regular dentist who happens to specialise in cosmetic dentistry: Dr Mano Soltan of Covent Garden Dental Clinic in Chandros Place in town. Price per implant? £1850.00: Half paid when you have the drilling done, the other half on completion of the process when the 'teeth' have been fitted. Just for info, mine are both molars, the big 'ol chewers, one on the top and one on the bottom.
Dental implants have now a days become quite common. Recently, my dad got his tooth implants from a local dentist Torrance. He became a regular visitor of him as he really liked the way he treated all patients.