25 isn't enough. If you can live on pasta and rice constantly then maybe. But I'd say you're gonna need at least 25 for food per week, and then if you go out once a week at least 10 quid for drinks.
I usually spend about 20 a week on food and 20 on going out/prinks. If you buy in bulk though it'll be cheaper in the long run. Depends how much you go out and how much crappy student food you're willing to consume really!