get quakeworld.
Nquake is a good package for beginners:
http://nquake.com/
Ezquake is the name of the quakeworld client.
Then when you have quakeworld go to www.quakeservers.net, find a uk server from the list, copy its ip address, then open up ezquake, type "connect ipAddressHere" and you're there.
Or that's one way to do it.