TENSIONS in the race for the Labour crown have risen ahead of today’s Scottish hustings as both contenders threw accusations at each other, which is likely to make for a heated debate in Glasgow this evening.

While Jeremy Corbyn, irritated by media questioning, defended his actions in the row over train overcrowding, the Labour leader hit out at his rival, Owen Smith, for appearing to brand him a “lunatic,” a claim strongly denied by the Welsh MP. Mr Corbyn said using such language was deplorable while his campaign accused Mr Smith of “degrading” the leadership contest by descending to personal abuse.

For his part, the former shadow work and pensions secretary, issued an apology for using the term but insisted he was referring to himself and not Mr Corbyn.

Read more: Jeremy Corbyn defends actions in train overcrowding row as Owen Smith suggests it was a political stunt

Mr Smith also went on to accuse his colleague of using the so-called “traingate” incident as a political stunt to make what he said was the legitimate case for renationalising Britain’s railways.

Mr Corbyn, who will give a speech and hold a rally in Glasgow ahead of the hustings, expressed annoyance when his keynote announcement to “renationalise” the NHS south of the border was overshadowed by more questions about traingate.

Asked by one reporter if he was a "liar" over the row and a "lunatic", Mr Corbyn replied: "I was hoping you were going to ask questions about the National Health Service but sadly you're not.

"I deplore the use of that language in any context; I don't use it myself and I don't use it today."

The Labour leader insisted the post-speech press conference was about the NHS but as further questions emerged on traingate, he became irritated and said: "Can we move on, please? We're discussing the NHS today. Can we have an NHS question, please?"

However, he then relented and was pressed about why he did not sit in unreserved seats which CCTV footage suggested were empty.

He explained how he was trying to find two seats for himself and his wife but could not. The train manager offered to upgrade them to first class but they refused and the party leader was videoed complaining about overcrowding while sitting on the floor of the carriage.

Read more: Jeremy Corbyn defends actions in train overcrowding row as Owen Smith suggests it was a political stunt

Mr Corbyn said later seats were found, adding: “We sat down there and we then conducted a lot of preparatory work for our visit to Newcastle."

Virgin Trains has said it was "puzzled" by the suggestion the Islington MP was unable to find unreserved seats when he boarded the train because CCTV images appeared to show "they're right next to him".

Sir Richard Branson, who co-owns Virgin Trains with Stagecoach, also got involved in the row on Tuesday, posting a link to the CCTV images on his Twitter account.

Asked why the billionaire had decided to make an issue of seating on the services, Mr Corbyn replied: "I'm very pleased Richard Branson has been able to break off from his holiday to take this issue as seriously with the importance it obviously deserves.

"I hope he's very well aware of our policy which is that train operating companies should become part of the public realm not the private sector."

Earlier, Mr Smith was asked if he thought his colleague had been lying about the train incident.

Read more: Jeremy Corbyn defends actions in train overcrowding row as Owen Smith suggests it was a political stunt

“The evidence is there on the CCTV footage,” declared the Welsh MP. “Obviously, Jeremy did have a seat and he went to sit on the floor in order to make a point about overcrowding. It’s a legitimate point to make…”

Meantime, Virgin Trains faces an investigation by the data protection watchdog over its release of the CCTV footage of the Labour leader to see if any legal rules about publishing data were broken.

Elsewhere, Len McCluskey, the Unite leader, again warned Labour’s autumn conference might not go ahead if a row over its security is not resolved. Showsec, the firm overseeing security at the annual event, is in dispute with the GMB over union recognition.