Contrary to my expectations, you're not immediately clapped in irons. Instead they take your registration, name and phone number, then you're allowed to go home and fetch your wallet. (It probably helps if you're a well-spoken white female on a comedy scooter.)
I didn't ask to have my Nectar card swiped; I didn't think it would go down too well.
Also I saw Darth Vader waiting to cross the road at the Florence Nightingale roundabout, so I'm not entirely convinced my day so far hasn't all been a dream.