Go to Silicon Drinkabout (http://silicondrinkabout.com or Hacker News London and talk to some startups. There are many highly funded startups that would love to have you on board. There are a number of big web startups in London with hundreds of employees and many of these founders go to these events.
As another user said http://hackerjobs.co.uk is also a great resource. Look past Twitter, Facebook, Google.