You will automatically own the copyright to anything you commit to paper (or any other recorded format). There's no formal system available (or, indeed necessary) for registering copyright:
http://www.ipo.gov.uk/types/copy.htm
However you can't copyright (or patent) ideas, per se.
In practice it's exceptionally hard to guarantee that your idea won't be 'borrowed' by someone else. Your best course of action might be to only reveal your idea to people who're prepared to sign a CDA (Confidentiality Disclosure Agreement):
http://www.ipo.gov.uk/cda.pdf
Chris