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.

http://www.ttapress.com/index.html

Site, guidelines and forum are pretty good.

They are also publishing the potentially brilliant Writers guide Success and how to avoid it. Looks good. I'm ordering my copy.