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. He is expected to say:
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.
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The former shadow business secretary Clive Lewis made the comments at an event backed by Momentum.