I worked on elevators for years and have ridden on top of lots of elevators at full speed. It can be dangerous, especially on the top floor due to shit hanging down in the overhead. But, he is generally safe because he's keeping his body parts away from the moving parts and sides. He's also on a very slow speed traction elevator. Fastest one I've been on top of reached speeds of 750 feet per minute.
To get on top of the car, he has lunar keys which he probably bought off the internet.
He knows quite a bit about elevator logic and controllers. Some of his terminology is off unless they use different terms in England. Pulley should be called sheave and manual should be called inspection.