Check out the rollerblade tricks section. Here there are tricks such as how to skate a barrel roll, how to skate a grapevine (originally from SkatingTutor.com), and learn how to use your heel brake, etc. etc. There's a bunch of links to other heel brake tutorials around the web on this page, and plenty of clear photos plus a video.
All Rollerblade reviews can be found here on LondonSkaters.com
Skate videos and rollerblade video clips at LondonSkaters.
See this page for inline skate retailers in London, and also some internet based shops.