There are a number of VAT rates applicable to the sale of food by the University. The underlying principle is that food (not catering) is zero-rated, but some foods, including ice cream, confectionary, non-alcoholic drinks and crisps are liable to VAT at 20%.
NB: Alcohol is always standard rated irrespective of whom it is sold to.
HM Revenue and Customs define catering as food consumed on the same premises at which it is sold, or hot takeaway food. Food that is provided as catering is standard-rated unless the catering is being provided to students.
Food or catering provided to students is exempt as a closely related supply to the education provided, see Supplies closely related to education. Students are anyone who is at the University for a course, seminar or similar, not just under or post grads.
Sandwiches sold for consumption off premises are not classed as catering and should be sold as zero-rated.