There are so many different aspects of the London scene I think you'd have to ask alot of different people to get the whole picture but I'll try to scratch the surface and tell you about some stuff I personally dig around here.
One of the most exciting things to recently start happening in the scene here is The Big Takeover: DIY punk shows in non traditional, adventurous places, mixed bills and in aid of a different cause each show!
On straight edge...I personally can only think of 3 straight edge bands that are actually based in London, those are...
90s style hardcore, musically in the vein of bands like Chokehold and Trial
Veganarchist thrashy punk with female/male duel vocals and members originally from all over the globe!
Thrashcore...Socially concious lyrics on topics such as vivisection and rape
Actually from the south coast of England but I'm including them 'cause they deserve a mention and Luke now lives in Kingston which is 20 minutes away from London by bus so.........
"Most hard working band in the UK" I think it's something ridiculous like 5/6 releases in the space of a year, 3 euro tours, countless weekenders and constantly playing shows in the UK even though two of them are at University, one is a fulltime businessman and I have no idea what Andy does other than grin a lot and be a lad.
Not a straight edge band by any means but a member of Hello Bastards now plays in Pettybone. Really new, all female line up consisting of ladies who play/played in Invasion, Honour Among Thieves and Hang the Bastard. I'm going to save myself the embarassment of trying to describe their sound as I've only see them play once and it's pretty hard to define anyway but they're recording in early August so keep your eyes and ears peeled.
The guitarist of Pettybone also has a cool blog focusing on women involved in the punk/diy/art scene.
Ultimately, of course like in any scene, there are good things and bad things about but I'm pretty excited about what's going on right now. Plenty of new bands, zines and labels popping up, alot of people travelling for shows all over the country. I think there's something for (almost) everyone to enjoy but if you're fed up of seeing the same generic bands play the same gloomy old man pub every week then get out there do something about it!