If you want a HE tournament try Gutshot. It is in North London.
http://www.gutshot.co.uk/livecardroom.php is their website. It is a friendly club and the competition is quite soft. They have cash games which generally start as soon as people bust out of the tourney.
There is a casino called the Vic in more Central London. I have never played in it.
Hope this helps. Feel free to ask any more questions.