Labour needs to remember its Blairite traditions as well as left-wing ones, leadership challenger Owen Smith is warning.
In his final key-note address of the election before ballots close on Wednesday, Mr Smith is expected to accuse the pro-Jeremy Corbyn Momentum organisation of "bullying and intimation" as he claims there is just five days left to save the Labour Party.
The Welsh MP was insisting the party needed to acknowledge its Blairite heritage as well as other strands of political thought.
"We are the party of Jeremy Corbyn and Tony Blair - not the party of Jeremy Corbyn or Tony Blair. And those of us who don't think of ourselves as either Blairites or Corbynites - which is most of us - are welcome in this party too.
"If we lie to ourselves about what this party is and has always been, if we choose to pretend that what we have all always stood for is something we have only just discovered, then we do an injustice to all of our predecessors in the Labour movement.
"And if we take pride in our narrowness as a movement, instead of celebrating the breadth of our Labour tradition and everything that we have achieved together, then we make it less likely that we can appeal to the public, and less likely that we can win. If we hate our own history, why should anyone else love it?" Mr Smith is telling activists in London.
The leadership challenger is accusing Momentum of behaving like a party within a party.
"With five days left in this race, there are five days left to save the Labour Party. Five days to save it from a leadership that's taking the party away from the concerns of the British people, away from credibility, away from unity.
"The very future of the party is at stake. Just as we had to fight Militant in the 1980s, we have to fight to save the party we love today. We know what's at stake, because they've started showing their hand.
"Momentum in Liverpool - some of them exactly the same people as were in Militant all those years ago - organising to deselect a Labour MP. Threats to MPs all over the country.
"A 'deselection list' circulated by Jeremy's campaign, attacking Labour MPs. Disowned by the campaign. Apologised for by the campaign. And then defended, on stage at this week's hustings, by Jeremy himself.
"It's part of a culture of bullying and intimidation that says to Labour MPs and Labour members that they have to shut up and get in line or get out. Exactly the same tactics used by Militant in the 1980s," Mr Smith is expected to say.