Try these links (some require a bit of looking to find the UK ones) from my bookmarks:http://www.placesforwriters.com/journals.html
http://www.saveourshortstory.org.uk/
http://www.route-online.com/
http://www.theedge.abelgratis.co.uk/index.htm
http://www.pulp.net/about/index.html#aboutus
There's not a whole lot of UK magazines, but your best bet is to go into a large-ish bookstore, that you can sit and read a book while drinking coffee, and pick up a copy of the UK Writer's Market -- copy addresses as needed...
EDIT: Sorry, I'm not sure if any of these are SF. I missed that in your post until now... still, you might find them useful.
[This message has been edited by HSO (edited March 23, 2005).]