18/08/2015 10:04 BST | Updated 18/08/2015 10:59 BST

RMT Boss Steve Hedley Calls Labour Leadership Hopeful Liz Kendall A Ukipper

Rick Findler/PA Wire
Steve Hedley, Senior Assistant General Secretary of the Rail, Maritime and Transport (RMT) union, makes a speech to members of the union protesting outside Paddington station in London, as train services on some of the country's busiest routes will be "significantly" hit because of a strike by rail workers.

The boss of one of Britain's biggest unions has given a blistering account of the Labour leadership contest, rubbishing both Andy Burnham and Yvette Cooper and denouncing lacklustre poll performer Liz Kendal as a 'Ukipper'.

Steve Hedley, general secretary of train drivers' union RMT, hailed frontrunner in the race to succeed Ed Miliband Jeremy Corbyn as "the only true Labour person" contesting the leadership, but gave a damning criticism of the Islington MP's three rivals.

In an interview with ex-MP George Galloway, Hedley claimed that Labour's shadow health secretary had "flip-flopped", first from being a 'Blairite' to a 'Brownite', before then conceding political ground to Corbyn in a bid to boost his waning popularity.

Rounding on Yvette Cooper, the union boss alleged she would be better suited to either the Conservatives or Liberal Democrats, while Liz Kendall, perceived by many as being the least left-leaning candidate, should leave Labour and instead become a member of Ukip.

jeremy corbyn

Corbyn is the favourite to be elected leader in September

"I don't think of any of them as true Labour people," he told Galloway in an LBC segment on Monday.

The controversial former Respect Party leader echoed Hedley's comments, branding Corbyn's competitors "a parade of speaking clocks".

"It's not just that Jeremy is good and true, and has stood the test of time, and deserves support for those reasons, but the opposition is really, really limited," Galloway deprecated.

"I mean if it were not for Jeremy, people would have fallen asleep long before by now. We have a parade of speaking clocks up against him!"

Hear the full interview below

The interview came as tensions between those trailing behind Corbyn intensified, campaign managers from both the Burnham and Cooper camps engaged in a bitter battle to position themselves as the candidate most likely person to beat him.

The shadow health secretary's campaign chief first called on Cooper's team to stop talking up the possibility of her becoming leader, arguing that “the Yvette campaign remains in complete denial as to the fact that they cannot possibly win”.

But her staff retorted with a fiery rebuttal, accusing their rivals of “old-style bullying from the boys” and adding it was Burnham who “needs to step back and leave it to Yvette”.