Labour doubled down on its pursuit of economic growth as the UK’s second largest union warned it could cut the funding it donates to the party unless more of its policy priorities are backed.

Sir Keir Starmer has renewed his defence of putting financial prudence at the heart of his plans ahead of a set of crunch by-elections in which the party hopes to inflict defeats on the Conservatives.

In an article for The Observer newspaper, the Labour leader said: “Frankly, the left has to start caring a lot more about growth, about creating wealth, attracting inward investment and kickstarting a spirit of enterprise.

“It is the only show in town for those who dream of a brighter future.”

He added: “Taking seriously the foundations of economic responsibility may not set people’s pulses racing, but the new country we can build on top of them will do.”

It is the latest attempt to pitch Labour as a party prioritising “financial responsibility” over spending due to a dire economic backdrop, a move which risks angering unions and the left.

Earlier on Saturday, Unite leader Sharon Graham warned Sir Keir there will be “no blank cheques” as she urged the party to be “bolder” in an interview with the BBC.

She told the broadcaster: “I want to see some movement if we are going to give what we usually give.

Sir Keir Starmer
Sir Keir Starmer speaking at the Unite Policy Conference on Thursday (Stefan Rousseau/PA)

“We would be better off with a Labour government but I am very, very disappointed with the lack of ambition.”

Ms Graham’s intervention came after she saw off a bid by some members of the union, which is Labour’s biggest financial backer, to end affiliation with the party earlier this week.

She said she is “very, very disappointed” by the “lack of ambition” at the top of the party and warned it was failing to offer a distinct alternative to the Tories as it tries to reassure voters it can manage the economy.

The union boss said “we need be as bold as the 1945 Labour government” which created the NHS, adding: “There wasn’t much money about then, I can tell you.”

Ms Graham told the BBC that strict fiscal rules have led to “inertia” which has prompted the public to question what the difference is between Labour and the Conservatives.

She also said Labour must “talk about what they can do to change Britain. People want something to vote for”.

“If Labour are saying what’s happening now is awful – and it is absolutely awful – they have to come out with solutions to that,” she added.

The BBC said she is pushing for renationalisation of steel and energy companies to be near the top of the party’s priority list.

During several meetings with the Labour leader, she said it would be cheaper to buy a steel industry that has lost much of its market value than to bail out its private owners, the broadcaster reported.

She told the BBC: “We will take our ideas to the people.

“The real decision-makers are the voters. If they push those ideas, politicians tend to move when they speak to voters

“People will say they remember when energy companies were privatised and when they paid massive bills, and it was a Labour government that stopped all that.”