You have to find out (just ask, I think) if they are taking NHS patients. I found a couple of dentists on the site that said they were, but then when I called, I was quoted the private prices and told they weren't taking new NHS patients. So, I kept calling around to make sure I was going to get NHS prices.
The place I go to is offers both, but the emphasis is on the NHS patients, so when they quoted me on all my work (and boy, do I need a lot!) it came under bands of treatment, so for this round, which includes a lot, the whole thing is coming to £198. The service isn't too different - (although expect less frills than your average NY dentist) but the appointments are shorter so I'm basically going on a weekly basis to finish up a root canal because they don't do it all in one (or two) appts like they would at home. The difference is (but I think this can be negotiated with your dentist, but I wouldn't count on it) is that it's definitely more focused on your dental health than your cosmetic smile, if that makes sense? I know the white fillings and crowns cost more at my place. If it's a back tooth, I don't care, but I don't want a tin crown on something that's visible in my smile. So there's that. But, I do think it's at the discretion of your dentist because I know a girl at work had the white filling at nhs prices b/c the dentist thought it would be visible when she smiled.
That, and the whole cleaning that would usually come at your first appt with a dentist is something you have to schedule with a hygenist at a seperate appt, and costs extra.