This page has links to A Level past papers and solutions. STEP and Oxford Admissions test links are at the end of the post.
Exam Solutions has thousands of worked video solutions to A Level questions. Note the tabs at the top of the site, select A-Level Maths and then your chosen exam board.
Revision by topic:
crashMaths AS Pure Maths Key Skill Checks
The Edexcel examining team have selected student responses to all questions from the trial of the Sample Assessment Materials. For each question, very clear mark schemes are given for that question and then a range of student responses with accompanying examiner comments on how the mark scheme has been applied and the marks awarded, and on common errors for this sort of question.
UK Legacy Examination Materials
OCR (MEI) papers & mark schemes
From David Smith:
OCR (MEI) C1, C2 & S1 papers and solutions
MEI Revision Videos – Further Mathematics Support Programme
AQA – questions by topic – The Chalkface
For an additional source of questions and full solutions for the Pure Maths content of A Level exams see MadAsMaths.
For an extensive collection of Challenging questions for Advanced Level students we can turn to the Oxford Maths Admissions Test, note the menu on the right hand side of the page, many papers and also solutions are available.