Yesterday, near Tooting Bec Common, a chap on an orange TNT delivery bike, with two full panniers. He was looking mildly confused, so I suspect wasn't sure where he was going, but I was late for work, so didn't have the time to stop and check up on him.
Later on, near Sloane Square, I saw a second TNT bike locked up and sans rider this time.
The bike is a chunky looking step through design, in fairly obvious orange, you can easily find images on Google. I'm not surprised if they're using them around central London, but Tooting Bec isn't the place I expected to find them.
Two in one day, after never seeing them before.