I'd say that's probably about right, but because I'm catered in John Foster my rent is £135 a week, so I spend more than the average.
I spend about £10-£15 a week at Asda (Bits of food etc for snacks and lunch, and if I miss breakfast; alcohol, plus shampoo and toothpaste and stuff) and then about £15 on going out; and £10 on random things like fancy dress or the odd treat when I go shopping!!
Having experienced many weeks of catered food now, I would recommend going self catered; I miss cooking, the food can be a bit repetitive and in hindsight I'd much rather have saved myself £40 (I know I could feed myself for less than that a week!!!)