Keeping your bike indoors helps keep it out of view from predatory eyes. Leaving a bicycle locked up in any one place for an extended period of time is never recommended, especially overnight (even if it is right outside your door).
The problem with this is bikes are a pain to store inside, especially if you live in a small flat in London, and even more of a pain for the flatmate who keeps knocking themselves on the handlebars.
Making your bike thin
Graham Hill, the founder of TreeHugger created a bike that all but disappears when stored in doors. Check out his video:
Graham uses the Speedlifter Twist handlebar gadget, which allows you to store your handlebars flat when not in use.
What do you use to store your bike indoors and out of the way?