Unlike the
USA,
universities in the
UK are rarely a collection of
colleges. The only universities (to my knowledge, and having researched which one to
attend only two years ago, I think I might know) are
Oxford,
Cambridge,
London, and
Durham.
Universities are institutions licenced by the Queen (i.e. the Privy Council secretariat) to a) Award degrees b) Call themselves universities. These are the only requirements. A college here (and in this context, for the term is also applied to non degree-awarding schools which kids don't have to go to unless they want to) is an institution franchised by a university to award degrees. For instance, University of Southampton used to be University College Southampton, a college of the University of London, like say SOAS. However, non-collegiate universities, like Bristol also franchise, so University of Gloucestershire used to be franchised by Bristol.
Colleges in collegiate universities (Those mentioned in the first paragraph) other than London, also do not award their own degrees. In these universities, colleges have certain administrative and pastoral roles (This phrase does not do justice to the importance of the colleges in these universities), while their academic staff will also be associated with various academic faculties and departments of the university. Degree certicates will not bear the name of the college that the student belonged to (Except at London, where colleges are much more independant).