So when I did my Access course in Engineering, and was applying to university, I found different unis had vastly different views on the course. I got into a Leeds, on a course at the time ranked I think 1 or 2 for the subject, but Sheffield wanted me to do A Level Maths and get an A as well as doing Access!
I also found that universities tended to interview Access students more often than A level students.
Oh, and when the course started, there were extra maths classes to get everyone to the same level that were offered to Access students (we could choose if we thought they would be useful or not), but the for BTEC students they were compulsory. The A Level students weren't offered them. Because of that, my guess is that the university views A level students to be the most able, then Access, then BTEC, at least in maths.