The leader of Labour’s biggest union backer said she would keep Sir Keir Starmer’s “feet to the fire” and claimed the party had been “too timid”.
Unite’s general secretary Sharon Graham said Labour had to make a “better offer” for workers.
With a general election expected next year, Ms Graham – who has frequently criticised the Labour leadership – said “we’re at the business end now” as she highlighted what she expected in return for support.
“But there’s a difference between limping into Number 10 and being carried in – actually carried in – there to say, look, actually this person is going to come in and they’re going to bat for us.”
She added that she was not “embarrassed” to make it uncomfortable for Labour by “raising issues like the renationalisation of energy, investment in steel, oil and gas” because “that’s my job”.
“So I’m going to keep Labour’s feet to the fire,” she said.
“I absolutely want a Labour government, of course, but I want a Labour government that is going to make real change to people’s lives. And I think at the moment Labour have been too timid.”
She said that after 13 years of “Tories batting for big business and batting for the rich”, it was “time for Labour to come in and bat for our side, bat for workers and bat for communities”.
With the prospect of former Labour leader Jeremy Corbyn – who has lost the party whip in Parliament – standing as an independent at the next election, Ms Graham said Unite could not support him.
“The support is for the Labour Party because that’s what our rule book says that we do,” she said.