If you look on IMCDB, you can see what Simon is on about.
Like you Simon, I did think it was a little silly. What I didn't understand was, why was that American riding round on the M20.
The army bike in episode four is a BSA, the civilian bike in episode six is a Norton.
I think, or rather I’m actually quite sure of it. But I could of course be wrong, I make mistakes on a daily basis.
One thing I did today that was not a mistake was to take my Bonneville out for a sunset drive over various bridges of Stockholm in the warm summer breeze. My M21 is in a state of slight dissemble for the moment, otherwise that would of course be my first choice!