As I understand it, he has no need to declare spent convictions, they are spent and should now be considered irrelevant. It is illegal to discriminate because of them (although admissions tutors undoubtably know how to discriminate without being caught).
The exception, is for specific courses where there is contact with vulnerable people (medicine, dentistry, nursing, etc.) or where the degree leads into a specific field (law, teaching etc.) where they may be expected to have a CRB check or a Enhanced CRB check.
If this is the case, he would be strongly adviced to declare this beforehand, with or shortly after application, to someone senior in the admissions department. It's likely that if it is a serious offence that could compromise his place that there will be a meeting to discuss his case, how that works depends very much on the university and the course.
'Serious' offences vary, for law, I believe that any offense other than traffic offenses are serious whereas for nursing, say, they would be more interested in violence and the like.
I'm not convinced that different universities have different policies, certainly there's no 'Cambridge won't take you, but Oxofrd Brokes might' kind of differentiation.
Some idea of crime and course would provide a more thorough answer.