LABOUR can only win the next General Election if it recovers in Scotland, Liz Kendall, the modernising candidate, has insisted as she and her fellow candidates clashed on how to deal with the phenomenon of Corbynmania.

The Leicester MP, speaking ahead of a campaign visit to Edinburgh today as part of a three-day 13 city whistle-stop tour of Britain, admitted reviving Labour’s fortunes in Scotland would be a “long, hard slog” but that it was essential if the winner of the contest was ever going to occupy No 10.

Asked if Labour would win in 2020 without the party – which lost all but one of its Scottish seats in May - reviving north of the border, Ms Kendall said: “No. We will have to win back support in Scotland...We had a catastrophic defeat, to put it mildly, but we also had appalling results elsewhere.”

She claimed Jeremy Corbyn was “unelectable” as Prime Minister, saying his “politics of protest and of the 1980s” were simply not right for a modern, outward-looking democracy in the early 21st century.

Three weeks ago, the Shadow Health Minister accepted her left-wing colleague was ahead but insisted “things will change”; they have but to her rival's advantage. A poll this week placed the former rank outsider more than 30 points ahead of his nearest rival, Andy Burnham.

Asked about Tony Blair’s annihilation warning, Ms Kendall said: “We are at a moment of real crisis. The great tragedy is our values and principles are needed more than ever before. If we vacate the pitch, we won’t be able to put those principles in practice; that will be a tragedy not just for the Labour Party but for the country.”

The frontbencher said she would not pull out in a bid to have just one Stop Jeremy candidate but would be in it “to the very end”. She made clear she would be using her second and third preferences and would be encouraging her supporters to do the same but declined to say who, between Mr Burnham and Yvette Cooper, she would support.

Ms Kendall admitted she had real concerns about the voter registration process, particularly given more than 150,000 people had registered in the final 24 hours before applications closed. But she explained: “I have not called for it to be paused like some MPs have because of the information I have had from the party about the checking process. But that’s going to absolutely have to continue particularly with all these new people, who have joined up.”

She added: “We will be keeping an eye on that.”

Jack Straw, the former Foreign Secretary, also entered the fray, warning that a victory for Mr Corbyn would condemn Labour to “perpetual opposition”.

Mr Burnham later took a thinly-veiled swipe at Ms Cooper and Ms Kendall, saying: “Attacks on Jeremy have misread the mood of the party,” which, he argued, wanted “something different; something more to say on the doorstep at election time”. The MP for Leigh near Manchester made clear his campaign would be “keeping it positive”.

The Shadow Health Secretary insisted the left-winger had "brought the campaign to life", noting how "there is a yearning out there for a different style of politics" and that people "want something bigger they can believe in".

He also claimed: "I am the only candidate in this race who can beat Jeremy Corbyn."

Meantime, the bookies’ “red hot” favourite, campaigning in Scotland, said critics who had resorted to personal abuse and attacks on his character were "nervous about the power of democracy".

Just hours after Tony Blair’s dire warning about a Corbyn victory, the London MP hit out at the "politics of celebrity".

He said: "This campaign is not about and never will be about personal abuse, name-calling, calling into question the character of other people or other candidates. Let's be adult about it. Let's have a serious debate.”

Mr Corbyn claimed Labour was still paying the price for the ex-PM’s decision to invade Iraq and pledged never to go to war "on behalf of whatever capricious US president happens to be in office at that time".