Keir Starmer has downplayed the prospect of tax cuts under a Labour government, and admitted he might have to roll back his £28billion green energy investment plan.

With the UK tax burden its highest for 70 years, the Labour leader said he wanted people to have more money in their pockets, but growing the economy would come first.

He also took a coded swipe at the SNP, saying nationalism was "exhausting" and "fueled by division".

In a speech outling his party’s plan for “a decade of national renewal” if it wins the general election expected this year, Sir Keir also cautioned voters against cynicism and apathy.

He said: “You can reject the pointless populist gestures and the low-road cynicism that the Tories believe is all you deserve. That’s all they have left now.”

He said he wanted to fight the election on the economy, would be willing to process asylum seekers off-shore, and would root out cronyism and sleaze.

Denying reports he wanted to duck them, he insisted he wanted to tak part in TV debates with Rishi Sunak, saying: “Bring it on."

He said: “We don’t just expect an election on the economy. We want an election on the economy and we’re ready for that fight, ready to close the book on the trickle-down nonsense once and for all.”

He pledged a “crackdown on cronyism”, with a message to politicians: “To change Britain, we must change ourselves”, adding: Nobody will be above the law in a Britain that I lead.

"With respect and service, I also promise this:  a politics that treads a little lighter on all of our lives.

"Because that's the thing about populism or nationalism, any politics fueled by division.

"It needs your full attention. Needs you constantly focusing on this week's common enemy. And that's exhausting, isn't it?"

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He said Labour’s biggest obstacle was public scepticism about politics.

“The biggest challenge we face, bar none, the shrug of the shoulder.

"Because this is the paradox of British politics right now. Everyone agrees we are in a huge mess. Services on their knees, an economy that doesn’t work for working people, even when it grows, let alone when it stagnates like now.

“Everyone agrees as well that it has been like this for a while, that Britain needs change, wants change, is crying out for change. And yet trust in politics is now so low, so degraded, that nobody believes you can make a difference any more.”

He said he offered "Project Hope" and a “new mindset” in government, so that Britain could “get its future back”.

South of the border, Chancellor Jeremy Hunt has brought millions of people into the higher rate tax band by freezing the threshold for the 40p rate at £50,000.

A similar thing happens in Scotland with the freezing of the higher rate (currently 42p) at £43,663.

Asked about unfreezing the tax thresholds, Sir Keir said:““I do want more people to have more money in their pocket. That’s a fundamental principle we start with.

But he added: “Any tax cuts have to be fair and affordable, and we have to be realistic about that. But I think the place to go is to growth on this. ”

Pressed on the point, said: “Before we get to the question of tax we’ve got to grow the economy. 

“The first lever that we will pull is the growth lever because in the end that’s the only way we’re going to get the money we need to fund our public services.”

He said he was “fundamentally opposed” to axing or reducing inheritance tax. 

“I don’t believe in tax breaks for those who are already well-off when there’s nothing on offer for working people. So, I wouldn’t be doing what they [the Tories] are floating.”

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Sir Keir also appeared to retreat from Labour’s pledge to borrow massively to invest in green energy and jobs, which the Tories have seized on to attack the party.

Labour promised in 2021 to invest £28bn a year until 2030 in green projects if it came to power.

But last year shadow chancellor Rachel Reeves said the figure would instead be a target to work towards in the second half of a first parliament.

Sir Keir today suggested the £28bn figure was essentially aspirational, as it would be contingent on the state of the public finances, and could be less.

Trying to neuter what he called “misconceived” attacks on the policy, he said the £28bn would be “ramped up in the second half of the Parliament, that it will be subject of course to any money that the Government is already putting in, and it will be subject to our fiscal rules.

“That means that if the money is from borrowing, which it will be, borrowing to invest, that the fiscal rules don’t allow it, then we will borrow less.

“It is very clear and that is why this attack is utterly misconceived on this."

Tory party chairman Richard Holden said Sir Keir had a "consistent track record of telling people whatever he thinks they want to hear on any given day”, and had flip-flopped over Brexit, scrapping tuition fees and nationalising industry.

He said the only thing certain about the Labour leader was the "£28billion black hole in his spending promises", which he said would mean a rise in tax for families.

Sharon Graham, general secretary of the Unite union, added: "Undoubtedly the country needs change and it is crying out for different choices to be made. It is now critical that workers and communities can see clearly what choices Labour is proposing.

“For example, Keir rightly says we are exposed on the international stage regarding energy. The choice that needs to be made in order to reduce sky high prices is for energy - and in particular the National Grid - to be brought into public ownership.

“Put simply 'project hope' will require serious investment. Relying on growth to generate that investment is not realistic. We have not had significant growth since the 1970s. If we depend on growth to fund all the investment we need it will only result in inertia.

“Britain needs a Labour Government - but it needs it to be serious about real change.”