zebo - //As the first stop was York apparently, anyone would be able to sit on the reserved seats, no-one else was getting on before than, and that of course presumes that he isn't lying through his teeth. //
I am unsure what you are saying.
You appear to be saying that all the reservations were from York onwards, which is extremely unlikely - a train leaving London is likely to be full of London travellers who have reserved seats, which is standard and sensible practice on a busy route like this one.
Obviously people were getting on in London, the film footage shows the train to be busy, but not full, which is the point of the argument.
Sitting on the floor and ignoring an available seat does not make the point for nationalisation of trains - Mr Corbyn would be better to find a Southern train into London in rush-hour - then he will have to stand or sit on the floor!