It was taken from inside a private courtyard, just outside my window, in a mews behind High Street Kensington. I never leave it outside, but was distracted and it ended up there overnight. It now looks like the attached, except that the handlebars are clad in red leather.
I was going to dimension the frame yesterday morning, so I can reproduce it just in this eventuality, but did not get round to it. Perhaps I can persuade Mike Burrows to share his frame drawing even if I doubt he will be interested in making another himself.