Essentially AS levels are half the A level so its half of the content of the A level and in terms of UCAS tariff points (a system where grades are worth points) the AS level is worth half of what an A level is. For example an A grade in an A level is 48 tariff points but in the AS level its only 20 points. Furthermore, AS levels tend to be a 1 year course whereas A levels are 2 years. AS levels aren't as common now as they used to be. At the end of the first year of A Levels students would take their AS level and then decide if they wanted to continue on to the full A level, the AS meant that they did not waste a year and came out with a qualification.
Yes, grade boundaries for both A level and AS level work the same as GCSE, meaning that they alter year by year and they can be found on the websites of each exam board. (I think that is what you are asking).
I am not fully aware of the specifics but my general understanding is that A Levels tend to be more academic with written tests and BTEC's are often more practical include coursework. They are also graded differently, so BTEC and Higher National Diploma (HND) are graded using Distinction, Merritt, Pass and U whereas A Levels follow A*, A, B, C, D, E and U But I am not the right person for this question.
Not really, Universities like that are very grade reliant. Unless the A level or GCSE grades were not achieved because of a reason that was eligible for special consideration, its quite unlikely those types of Universities would still allow entry since the offer your given by the university is the minimum grade they will allow you to become a student with.
Hope this helps
