It is honestly up to the University and their quota of intake (unless it is Oxbridge who have a reputation for outright rejecting those who failed to get AAA/A*AA). I know of a girl who achieved BBC and took up a place at RHCL for geography (despite her offer being ABB), and another girl who achieved A*A*B and was rejected for English Literature at Bristol, Warwick and the Exeter campus of Exeter University (whilst there were other people at my sixth form who got into the same course through clearing with much lower grades). The reasons that were provided for both candidates were both centred around the university's quotas, and their need to fill the courses for financial reasons.