Labour leadership contender Liz Kendall has warned criticism of party modernisers as "Tories" is a term of "abuse" that risks paralysing the party.
Ms Kendall, who has staked out her position on the centre-left, has been subjected to fierce criticism online from supporters of left-wing frontrunner Jeremy Corbyn, being labelled "Tory", "Tory-lite" and "Red Tory". Andy Burnham and Yvette Cooper have also been on the receiving end.
But in a speech tonight, Ms Kendall, in fourth place in the polls, says the attacks have become "a substitute for being forced to think".
Her argument that Labour must be "fiscally responsible, economically credible and passionate about championing opportunity, devolving power and a Britain that is open to the world" has been "derided as Tory or Tory-lite".
"Let me take this argument head on," she says. "Real Tories want to destroy trade unions and rights at work, abolish student grants, cut working tax credits for the low paid, and slash the role of the state for ideological reasons - not reform it so it is fit for the future. This is a huge mistake.
"But calling ideas from people who have been members of the Labour party for decades 'Tory' has become a term of abuse that is a substitute for being forced to think. And the real problem with this accusation is not its absurdity but the danger it poses for our Party."
She argues Labour has to "change how we apply our values as the world around us changes" but being called "a pale imitation" of the Conservatives "only helps the Tories by keeping Labour wedded to outdated solutions whilst the people we seek to serve move on and move away".
"Calling those who dare to think differently Tory-lite isn’t just a misguided insult. It is an enormous strategic mistake," she says.
Ms Kendall argues everything the party has achieved is through winning elections, and the party must win over people who voted Conservative: "I don't believe people who voted Conservative in 2015 or 2010 are our enemy."
Of the last Labour government, she says: "Compare what we did in 13 years of Government to what we achieved in the past five years of opposition.
Celebrities backing and attacking Jeremy Corbyn
ATTACK: Robert Webb(01 of10)
Open Image ModalThe Peep Show actor said: "He's a nice guy, totally marooned in 1980s politics. And I remember the 1980s very well. The Bennites f****d Labour. And then we had 17 years of Tories. Lots of people suffered while the Left kept their splendid principles. F**k that. Come on, guys." (credit:Zak Hussein/PA Archive)
BACK: Charlotte Church(02 of10)
Open Image ModalThe singer said: "He is one of the only politicians of note that seems to truly recognise the dire inequality that exists in this country today and actually have a problem with it. There is something inherently virtuous about him, and that is a quality that can rally the support of a lot of people, and most importantly, a lot of young people." (credit:Daniel Leal-Olivas/PA Wire)
ATTACK: Tony Blair(03 of10)
Open Image ModalThe former Prime Minister said: "If Jeremy Corbyn becomes leader it won't be a defeat like 1983 or 2015 at the next election. It will mean rout, possibly annihilation. It doesn't matter whether you're on the left, right or centre of the party, whether you used to support me or hate me. But please understand the danger we are in. The party is walking eyes shut, arms outstretched over the cliff's edge to the jagged rocks below." (credit:JUSTIN TALLIS via Getty Images)
BACK: Maxine Peake (04 of10)
Open Image ModalThe actor said: "For me Jeremy Corbyn is our only beacon of hope to get the Labour Party back on track, get the electorate back in touch with politics and save this country from the constant mindless bullying of the vulnerable and poor. Aspirational? Surely we should all aspire that everyone living in this country has the right to a decent quality of life." (credit:Matt Crossick/Matt Crossick)
BACK: Brian Eno(05 of10)
Open Image ModalThe musician said: "Corbyn has a story that people want to hear. It’s positive – idealistic even – but it isn’t outlandish, although the neoliberals would like you to think it is." (credit:Michael Crabtree/PA Archive)
ATTACK: Alan Johnson(06 of10)
Open Image ModalThe Labour grandee said: “In my view only Yvette Cooper can unite the party to win again. Those members who can’t give her their first preference should give her their second. After over a century of male leaders we have an election where the most qualified candidate to lead our party back to government happens to be a woman. Let’s end the madness and elect her.” (credit:Dominic Lipinski/PA Wire)
BACK: Mary Beard(07 of10)
Open Image ModalThe scholar said: "If I were a member of the Labour Party, I would vote for Corbyn. He actually seems to have some ideological commitment, which could get the Labour Party to think about what it actually stands for." (credit:John Stillwell/PA Archive)
BACK: Ken Loach(08 of10)
Open Image ModalThe film director said: ""Jeremy Corbyn, true to the best traditions of Labour, has a realistic plan to build new homes. Councils should have the power to plan and build good houses, environmentally sound, with proper infrastructure. Labour had the best Housing Minister ever in Nye Bevan. It's time for another with the same vision." (credit:Thibault Camus/AP)
ATTACK: Polly Toynbee(09 of10)
Open Image ModalThe Guardian journalist said: "Labour people, motivated by the plight of the needy in a grossly unjust society, shouldn’t gamble the future of the weak on such a slender chance. Every Tory government impoverishes the poor and enriches the wealthy. Every Labour government makes landmark social progress. Winning next time matters desperately. A Cooper leadership offers an infinitely better hope of success." (credit:Ben Birchall/PA Archive)
BACK: Owen Jones(10 of10)
Open Image ModalThe Guardian journalist said: "He is the very antithesis of the negative caricature of an MP: he’s defined by his principles and beliefs, uninterested in personal self-advancement, and determined to use his platform to further the interests of people and causes that are otherwise ignored." (credit:Rob Stothard via Getty Images)