Blimey - I wasn't 100% convinced myself! The IoW link did help to get me thinking in what turns out to be the right direction. Then I realised the viewpoint in the photo would be about right for someone in the r/h seat. The baffled clue, incidentally went right over my head.
Thanks TheiC for a great challenge - it was fun!
Now please excuse me while I rush off to find another...