As Edexcel Pure Maths

Yes it is possible to study As Maths and enter for the exam as a private candidate although i am not too sure what you mean by 'starting from the end of contents'. Do you mean working your way backwards through the spec?

Anyways there is plenty of resources available online to help you learn and practice the subject content:

1. Dr frost maths - This is what my teachers use to teach us. It has powerpoints for all the content for the edexcel specification and explains what you need to know very well. I would use these as a starting point and refer back to them if you are struggling on something.

2. A-level maths revision - I only discovered this website recently. It has notes for the subject content with examples as well as teaching videos. I feel it is really good and it has exam question by topics which are suitable for all boards as there is a lot of crossover.

3. exam solutions - The most commonly used website by A-level math students. It has tutorial videos and exam paper walkthroughs. I highly reccomend using this website

4.Tlmaths - This dude is a legend. He has videos separated by topic and gives loads of key examples and content for AQA, edexcel and OCR MEI. He also has exam paper walkthroughs which are useful