where in london is it best to study film?

i´ve been studying non practical cinema for two years, and am now intending on studying film in london. i´m wondering which film schools are known to be the best, and haven´t been able to find an internet site in which there is reliable rating of the schools.

if anyone has any direct knowlege of the issue, or reference to a site which holds such grading, it would be very helpful...