Some North west groups
In Manchester, there's a group called NWDC - North West Digital
Community. These guys try to co-ordinate the dates of events across
the whole NW region.
You've got Manchester LUG at http://www.manlug.mcc.ac.uk/
If you want to appeal to the slightly more hardcore of the Linux
people, look at Manchester BSD Users Group (mostly Unix Admins)
http://www.bsdgroups.org.uk/manchester/
For people who use Open Source Software already - take a look at the
list created by the MDDA (Manchester Digital Development Agency)
http://www.manchesterdda.com/usergroups/
If you're not already talking to them, have a chat with the guys who
run lug.org.uk to get your name on their server - the details are on
their front page, and also join the lugmaster list, for us who
currently or previously have run LUGs.