The Unite leader has been at odds with Labour in recent weeks
Unite leader Len McCluskey is to warn Ed Miliband his party reform plans will fail unless he does more to distance himself from New Labour.
Mr McCluskey will back the Labour leader’s proposals to transform the party’s trade union links in a speech to the Durham Miners’ Gala.
But he will say Mr Miliband must show union members he is “on their side”.
And that means distancing himself from the coalition and the “Blair-Brown years”, he will add.
Mr Miliband unveiled plans to shake-up Labour’s relationship with the unions in the wake of allegations that Unite tried to rig the selection of a Labour candidate in Falkirk.
The Conservatives seized on the row to claim Labour had been taken over by the union – its biggest financial backer.
Mr McCluskey denies his union acted improperly but stepped back from his war of words with the Labour leader by welcoming his reform proposals.
On Saturday, he will say he is ready to discuss Mr Miliband’s reforms if they can “re-engage” his members with the Labour movement and its political objectives.
But he will warn that Labour “can only exist if it remains the voice of ordinary working people” and argue the party – which has accepted the coalition’s spending cuts for 2015-6 – must change economic direction if it is to retain union support.
“Ed Miliband has now announced the biggest ever shake-up in the trade union Labour link – a link over 100 years old,” he will say. “Yes, it’s a gamble – change worth having always is.
“But if we are to go out and convince thousands of working class men and women that they want to sign up to be associate Labour Party members they will not be interested in the rule-book, or even the history.
“They will want to know – will Labour make a difference?
“Will the next Labour government reverse the present coalition’s disastrous policies? Will it be different not just from Cameron and his crew but from the Blair-Brown years as well?
“If we can say ‘Yes, Labour has learned, and Labour is on your side’ then this scheme will work. But if our people – our members – are unclear as to the answer then no amount of persuading will get them to sign up.”
Mr McCluskey will again defend his union’s actions in Falkirk, saying “the political class has become adrift from ordinary people and has failed to offer an alternative to austerity”.
“The parliamentary Labour party today does not look like, or think like, the working class communities it seeks to represent.
“That is a serious problem….That is what Unite was fighting for in Falkirk – to give the working class a stake in our democracy. I make no apology for that.”
Mr McCluskey has previously warned Labour that it will lose the next election if it offers the voters a pale imitation of the government’s deficit reduction strategy.
The Labour leader wants to overhaul the current system of union funding, in which members of supportive unions pay an automatic levy to Labour, unless they choose to opt out.
‘New political project’
In future, only those union members who “deliberately” chose to join the party in future would make contributions but unions have warned the changes could lose the party millions of pounds and may be unworkable.
TUC General Secretary Frances O’Grady will use her Miners’ Gala speech to claim union donations are the “cleanest in politics”, and argue for greater representation of ordinary workers at Westminster.
Rail union leader Bob Crow will, meanwhile, urge trade unions to set up a new left-wing alternative to the Labour Party.
He will say: “If others want to stick around and be insulted by those whose only interest is our money and not our ideas then that’s a matter for them, for the rest, there is a whole world of opportunity outside the constraints of the Labour Party and RMT would urge them to embrace it and join us in this new political project.”
Mr Crow – whose RMT union was expelled from the Labour Party – is reported to be in talks with the Communist Party of Britain and other-left wing groups to re-launch “No2EU – Yes to Democracy” to fight next year’s European elections.
The anti-EU party, set up with RMT funds, contested the 2009 European elections, but gained just 1% of the vote nationally.