In terms of flying an aircraft, nothing has changed since you stopped flying in 2000.
However, it sounds as if your PPL licence is not valid any more and that means you have to renew your licence before you can fly as PIC.
It is pretty straight forward on what steps to take and this has been clarified in several threads in this forum. So do a search and your hits will be high on this topic.
Basically, you need to get an examiner to test your skills to command an aircraft and then sign you off. For more information, check CAP 804 and search the forum.
WP