So then, I reckon that on the 'payment confirmed' page you would need to have a script that changes a database value (to 'Y' for example) which then allows access to the protected content based on that value.
How do you think it's best to set up a system that will automatically notify an administrator when a users annual access is almost over and they have to renew? I thought initially a CRON job could be set up on the server, which checks the database once a day and somehow does this with Universal Email?