Simon,
Whirly is quite right - if you're flying from anywhere south east of London then the temptation to pop over to France is going to be pretty irresistible once you have your licence. It's actually more straightforward to fly over there for a day's outing from Biggin/Redhill/Rochester/Lydd etc. than it is to get to most places in the UK from those fields, given all the restricted airspace around London.
Depends what you're interested in doing of course, but from where you're based you will probably come to think of north eastern France as part of your local flying area. The airfield lunches are certainly better, though I've yet to try Kemble's new restaurant.
I did my training on microlights and then got an NPPL when that came out because it was close to being a free upgrade from the microlight licence. I cross the Channel a lot in the microlight, but can't in a SEP (Single Engine Piston aka light aircraft aka 'A' Group). This is annoying, so I'm now upgrading to the full JAR licence. Still, doing the NPPL got me into the air in metal aeroplanes sooner so it hasn't been wasted.
There is a nasty catch to be aware of if you do consider the microlight route. Unless your training is done at a CAA registered facility by an instructor with a JAR FCL qualification as well as a microlight one, then you won't get the 30-hour credit towards a JAR licence if you do decide to upgrade later. Finding a microlight school which meets these conditions could be tough.
There's no problem though if you train from the start in a light aircraft for an NPPL with SEP rating. If you decide to upgrade, you'll get 30 hours credited leaving 15 more to do. You could use that time to do things like a night qualification, a tailwheel conversion, an aeros course or whatever.
The Class 2 medical isn't such a big deal if you're in reasonable nick. It may actually be more straightforward than explaining the NPPL requirements to your GP, plus you get a nice nurse smearing goo all over you for the ECG!
I got my Class 2 done by a good chap in Crawley - send me a private message if you want the contact details.
You've already had good advice on schools above. Go round and visit some and see which one you like the feel of. They range from places filled with people wearing ties and epaulettes to sheds in the corners of muddy fields; you just have to go and see where you're most comfortable with the atmosphere, the instructors and of course the fees.
Good luck!
PS - I can endorse Genghis' comments about Lydd - it may be a slightly bleak spot location-wise, but the club is a very warm and friendly place. It's quite a long drive for me, but I think it's worth it. Cubair at Redhill seems a good place too - I'm thinking of having a go in their Cub once the runways dry out or they fit floats to the aircraft! And Rochester is worth a look as well. Nice airfield which could do with more support to help ward off the threats from their local council.