The Imperial MSc Math and Finance is very good. I think its the best by far. You will be taught by some the best academics in the UK (inc. Mark Davis and Claudio Albanese) and there is an external summer project (i.e. a placement).
Check out the program, it is quite varied and has many options.
Warwick has some relatively famous names as well: Nick Webber, Joanne Kennedy, Antony Neuberger (godfather of var-swaps) and Stuart Hodges (not really sure if he's still there). Imperial does have the advantage of actually being somewhere (London) though, rather than in the middle of nowhere like Warwick!