I think there is a case for some form of re-testing to be introduced. I have a full driving licence for a car and a motorbike, I have held both for well over 40 years. While I have driven and continue to drive a car, I haven't driven a motorbike for about 30 years. I think the biggest bike I ever owned was a 250cc BSA capable of a top speed of about 50mph. Looking at todays monster bikes I could legitimately go out and buy a 1200cc bike capable of speeds well over 100mph which I would have no idea of how to drive and control, but I wouldn't be breaking any laws !!