Ed Miliband has become the first Labour leader since Neil Kinnock to address the traditional Durham Miners' Gala.
His appearance at the event, which is 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 say there was a crowd of over 100,000 people, with trade union members from around the country swelling the numbers.
Mr Miliband attended with his family and used his speech to launch an attack on the "divisive" policies of the Tories in government.
He said: "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.
"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 says his appearance marks a return by Labour to the politics of the 1980s.
She said: "By breaking 23 years of silence from the Labour leadership at the Durham Miners' Gala, Ed Miliband is handing his party back to Kinnock.
"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."