The main website in the UK where you can get information on UK Spam laws is:
www.informationcommissioner.gov.uk
To have a look at the actual government legislation then the following link is what you are after. (Check Para 22)
Law on UK Spam and Unsolicited Email
For a nice easy to read breakdown on the laws mentioned above have a look at.
December 11 2003 Guide to UK Spam laws