Not a crossword clue - just something I actually saw. A locomotive, going backwards (on a low-loader), down the M4, this afternoon.
It had the number 5552 on the side. A little searching suggests it to be locomotive GWR Prairie 5552, now belonging to Bodmin & Wenford Railway. I honestly never, ever, ever thought I would be trainspotting in cyberspace. Ever.
As for the photo ... harrumph, hem hem, yes, let's assume it was taken by a passenger who wasn't driving, shall we?