For postgrad degrees you apply direct to the university that interests you. The MPH at KCL is relatively new (been going about three years I think) and I don't know anyone myself who has done it but it'll certainly be reputable. The course at the London School of Hygiene and Tropical Medicine has been around for a very long time - check out the website for up-to-date info - the people I know who have done it liked it; it does have a substantial international perspective which not all of them do. Also, there are related courses like the Master's in Health Sciences at St George's Hospital Medical School - this gives a good general overview but doesn't provide the depth in the technical subjects (ie epidemiology and statistics) that you might be looking for. Are you fixed on London? What is your particular interest in PH?