In reply to veteye:
I did cycle on the M25 in Hertfordshire before it opened to motor traffic.
I later used to go from Cambridge to Harrisons Rocks for an evening climbing when the Dartford tunnel first opened.
And the M11 lacked speed cameras and I had a BMW.
But just before the whole m25 ring joined up, there were some nasty bits of A25 and the road down the Darenth valley where an old A-road was taking motorway levels of traffic. The roundabout with the duckpond in the middle at Otford was particularly dramatic.
My sons got their motorway driving practise on the M25 in rush hour, on the basis that if they could do that they could do anything.