The government is currently reforming the delivery of A levels moving towards a linear system, where all the main exams will take place at the end of the two year A level programme, without re-take opportunities. AS level exams will be available in these subjects but the AS mark and grade will not count towards the full A level qualification.
Since the year 2000, students have sat AS level exams at the end of their first year under a modular system of A levels. These exams count for 50% of the final A level grade with the A2 year accounting for the other 50% and with the opportunity to retake the AS level to improve the overall mark. These are the qualifications that are being gradually phased out.
We are currently in a transitional phase. This means that some A levels will take a linear form, whilst others will continue on a modular basis in which the AS level grade at the end of the first year will still count towards the final A level grade.