CCTV footage has been released appearing to show Jeremy Corbyn walked past empty train seats before he was filmed sitting on the floor complaining about the "completely ram-packed" carriages.
The Labour leader was travelling on the three-hour Virgin Trains service from London to Newcastle on August 11.
A video emerged last week which showed Mr Corbyn sitting on the floor, reading a newspaper, and saying "This is a problem that many passengers face every day" before calling for public ownership of the railways.
But Virgin Trains has released CCTV images which appear to show him and his team walking past empty, unreserved seats before the filming began.
The train operator's footage also shows Mr Corbyn sitting down in an empty seat more than two hours before reaching Newcastle.
A Virgin Trains spokesman said: "We have to take issue with the idea that Mr Corbyn wasn't able to be seated on the service, as this clearly wasn't the case.
"We'd encourage Jeremy to book ahead next time he travels with us - both to reserve a seat and to ensure he gets our lowest fares - and we look forward to welcoming him on board again."
Mr Corbyn was on his way to debate with Owen Smith in a Labour leadership hustings in Gateshead.