Last summer I was offered AAB (in Maths , FM and Physics) or AAA in three A2s to include Maths by Warwick to get into their Maths and Physics course.Got ABB in Maths , Further Maths and Physics due to screwing up some of my final modules including a D in one Physics practical and C in FP3) .
It took a while for it to be confirmed but I didn't get the place in the end - one of the things I remember them saying on one of the open days is that they made the offers with the expectation that most candidates would meet the conditions without too much difficulty.So despite missing my offer by one grade (and having As in M1-3) they must have had quite a few people who had no trouble meeting their offers.
Having said all that I know someone here at Nottingham got BCC for our Physics course (standard offer AAB) and still got let in despite massively missing the offer , and also I heard Mathematical Physics was struggling for numbers last summer having to enter Clearing.
In short if you miss your offer it depends on the demand/competitiveness of the course and whether they have enough people who met their offer or not.