Hi Smudge,
I'm not in London so I can't give you any specific advice. But in terms of general advice -
1 - Invest in pads. You will need a minimum of knee pads, elbow pads, and wrist guards. Possibly a helmet too.
2 - I would suggest checking out nearby rinks, and start there, if possible at a quiet time of day. Skating is much easier to learn on a smooth surface, than on road / path surfaces, which can be quite rough. They make look smooth when you are walking on them, but you soon find all the imperfections when you skate them. Good for the thighs, but hard work when you are learning! You'll have to decide if you prefer that to facing possible crowds at a rink.
3 - Depending on your financial situation, sometimes the gear can be quite expensive to buy all at once. It is one of those hobbies that lots of people think 'looks cool' so they start and then give up quickly. So, if you don't mind second hand, somewhere like ebay can be a good place to pick up gear really cheaply to start with, and then you can upgrade later.
4 - I don't really have any 'techniques' I can share. Just start slow (well, not too slow, you need some momentum to skate, but don't hurl yourself around), wear pads to start with, and just keep practicing.
Good luck, I hope you enjoy it. 