The blue touch paper lit, I decided to sit back and observe! As predicted we have thrifty or sometimes greedy hauliers, ‘luddite’ unions, established digs, stoic board-across-seat die-hards and tradition as our choice of elephants in the room on this one. There will be all sorts of factors that make up the mosaic on history on this. A contributory factor will be absence of legislation against sleeping in a wagon without a sleeper cab. This was, I believe, remedied first by Germany in (someone put me right here) the late '60s or maybe very early '70s. The knock-on effect of that will undoubtedly have had an eventual impact on UK wagons transiting Germany and mainland Europe in general. Only nine and a half pages to go to Xmas! 
Robert