Ed Miliband will today become the first Labour leader since Neil Kinnock to address the traditional Durham Miners' Gala.
His appearance at the event - billed as the largest remaining working class demonstration in the country - has been warmly welcomed by local trade unionists and party activists.
But the Conservatives said he was "cosying up" to Labour's left-wing union paymasters who secured the leadership for him.
Organisers are expecting a crowd in excess of the 100,000 who attended last year, with trade union members from around the country swelling the numbers at the old Racecourse.
Marchers will gather behind up to 80 banners, with over 50 brass bands playing at the Gala - more than in the 1960s and 1970s when the Durham Coalfield was still in operation.
Mr Miliband, who is attending with his family, is expected to use his speech to launch an attack on the "divisive" policies of the Tories in government.
"A few years ago the Tories tried to say 'We're all in it together'. But now we know they never meant it. Because we have seen what they do when they get back in power," he is expected to say.
"One rule for those at the top and another rule for everybody else. They cut taxes for millionaires and they raise taxes on pensioners. It's business as usual in the banks and small businesses go under.
"They try and divide our country between rich and poor. Between north and south. Same old Tories. Not building for the future but ripping up the foundations. Not healing our country, but harming it. Not uniting our country, but dividing it."
However Conservative Party co-chairman Baroness Warsi said his appearance marked a return by Labour to the politics of the 1980s.
"By breaking 23 years of silence from the Labour leadership at the Durham Miner's Gala, Ed Miliband is handing his party back to Kinnock," she said.
"Red Ed is using the Durham Miners Gala to cosy up to his militant, left-wing union paymasters. He's still driving the Labour Party away from the centre ground of British politics."
Dave Hopper, secretary of the Durham Miners' Association which organises the meeting, said it was only right the Labour leader attended.
Mr Kinnock was the last to speak at the Durham Miners' Gala in 1989 but "All those jokers before him should have come too," Mr Hopper said.
"In a county that is totally Labour-controlled and where every MP since time immemorial has been Labour, Blair, Brown and Kinnock refused to come. It was an insult to the voters in the county. "We are pleased Ed Miliband will be here, he has broken the trend and long may it continue."