Sir Keir Starmer has been urged not to backtrack on his plans to invest £28 billion in green projects, by Labour’s Greater Manchester mayor Andy Burnham.

He told the Labour leader to “stick to your guns” after Sir Keir said he may scale down the investment given the financial picture he would inherit if he becomes prime minister.

Mr Burnham said it is “not spending, this is investment in the future”, as Sir Keir faces pressure over the planned annual green payments.

This is not spending, this is investment in the future, investment in new industry, investment in better homes for our residents, better transport

The Conservatives have been increasing their attacks on Labour over the proposal after the UK entered the election year, but supporters have been concerned about watering down the key pitch.

Mr Burnham told LBC’s Tonight With Andrew Marr: “I would absolutely say to the party, stick to your guns, you’re on the right path.”

The mayor said the investment could reindustrialise the North and make the nation a “clean energy superpower”.

“That is about building future prosperity. This is not spending, this is investment in the future, investment in new industry, investment in better homes for our residents, better transport,” he said.

Mr Burnham conceded that “you don’t need to spend that level straightaway, you can build up to it”, but warned that “the more we delay” the more other governments will win the green race.

But Chancellor Jeremy Hunt said “you have to pay debt interest on the £28 billion whether you call it ‘spending’ or ‘investment’”.

“Money is money… and on this scale can only lead to tax rises,” the Chancellor said.

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

But last year shadow chancellor Rachel Reeves said it would instead be a target to work towards in the second half of a first parliament, if Labour wins an election.

Sir Keir last week described the policy as a “confident ambition” rather than a commitment.

He said that Labour sticking to its “fiscal rules”, which include making sure debt is falling, was more important than hitting the green spending target.

“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,” he said.