hey guys, obviously when I talk about London I take in account the Greater London. If you are a Ph.D. student, if your scholarship is good and could afford to live alone, at most you can let a studio flat in zone 4,5 or 6. My University is not in Central London, so I don't need a flat there. In zone 6, west london, with 500£ you can find really luxury place to share with 1 or 2 flatmates.
The point is: rent a studio and save 50£ or share a flat and save much more.
About food, by my own experience I need around 40£ per week + 10-12£ per week when you have lunch at the Uni. Going out..about 30£ per week. In zone 5-6 you can live quite well spending about 800£ per month (housing inclusive).