Jeremy Corbyn was mocked on social media after his claim that he was forced to sit on the floor of a packed rail carriage was challenged by Virgin Trains.
Labour leadership rival Owen Smith joked that his own campaign remained “on track” and he was “proud to be standing up for ordinary people”.
Former shadow cabinet minister Chris Bryant, another critic of Mr Corbyn, said: “I think the wheels just came off Jeremy’s campaign and he’s about to be shunted into a siding.”
A video emerged last week which showed Mr Corbyn sitting on the floor of the London to Newcastle service and declaring “this is a problem that many passengers face every day” before calling for public ownership of the railways.
But Virgin Trains released CCTV images which appear to show him and his team walking past empty, unreserved seats before the filming began.
The row, swiftly dubbed #traingate on Twitter, saw Virgin supremo Sir Richard Branson tweet a link to the footage saying: “Mr Corbyn & team walked past empty unreserved seats then filmed claim train was ‘ram-packed’.”
Jack Grant joked: “And they said Corbyn couldn’t win seats.”
But supporters of Mr Corbyn rallied around the leader, claiming that all the seats the leader allegedly walked past had been reserved or even claiming it was footage from a different train.
Mr Corbyn’s support for renationalising the railways was highlighted as a possible motive for Virgin’s response to the Labour leader.
Twitter user Chris Lowe said “billionaire with rail monopoly attacks socialist’s attempt to nationalise his racket”.
Charles B Anthony, who filmed the original footage of Mr Corbyn on the train, said: “Corbyn wants to renationalise their business. You do the math”.
He posted a series of images of the Labour leader chatting to other passengers forced to sit on the floor and footage of him walking through a carriage where the seats were occupied.
He said the Virgin footage of Mr Corbyn sitting in a seat was from after the Labour leader had filmed his video message on the floor, once the packed train had emptied out.
Supporters of Mr Corbyn have been known for their vigorous support of the leader on Twitter and Facebook, but have occasionally been too keen to attack the “mainstream media”.
After a rally in Liverpool, supporters of Mr Corbyn demanded to know why the huge crowd shown in pictures was not being given sufficient attention by the media - only for it to emerge that the photo was of the victory parade following Liverpool FC’s Champions League win in 2005.