Empires ok, quite expensive though, mainly due to its position. Great when WSOPE is in town though.
The International would probably be my choice, you can get sponsored easily enough to join.
http://www.theintclub.com
The Fox Poker Club should be good but has been slightly delayed in opening.
http://www.foxpokerclub.com
Obviously the Vic is known as the home of poker in London and is well worth a visit but beware the sharks.
There are quite a few others and if your after tournament poker, the The LPC is a must (I ought to play one day lol).
http://www.lpcpoker.com
I'm just a country boy so don't get into town that often.