How can I get a game tester job in London England

Google is your friend. Just type in games tester job London or whatever, and apply for all the ones you can find. Make sure your CV is up to scratch though :)

90% of getting a job in the Video Game industry is the same.
I will assume that you have a good resume, cover letter, experience, references, etc.. If you need Game Tester Training, there is some offered by Powerupgames.com.

Go to the IGDA or other sites that have the lists of publishers by area.
Find the publishers in your area.
Drop by and drop the items mentioned above. Ask how you can submit an electronic copy...
Followup with an email with electronic copies.
Repeat until you get something.