Probably didn't happen.
The claim that a family moved has only been made by Corbyn's aides, with nothing to back it up.
So far the only entities claiming that there weren't any seats are Corbyn and his aides.
And the (only?) reason it matters because his entire schtick is honesty - without that he's nothing.
Which is of course why this was a bloody stupid stunt and he should damn well have known better - do it on a Southern train for example.
Biting the hand that feeds IT
