Labour’s £28 billion a year green investment plan could skyrocket to at least £35 billion, Jeremy Hunt has warned.
The Chanceller said Treasury costings show that Sir Keir Starmer’s policy of upgrading insulation on millions of homes would clobber taxpayers.
The analysis concluded that the bill would be more than double the Opposition’s £6 billion a year estimate, at around £13 billion.
Labour branded the claims “ludicrous” and suggested the details of their policy differ.
The row erupted as Labour divisions within the party over whether the policy is affordable deepened.
Sir Keir said on Tuesday that he was “unwavering” over the party’s plans for cleaner energy by 2030, denying they were being scaled back.
But shadow chancellor Rachel Reeves has warned that an incoming Labour government might not be able to finance the cash injection.
Ministers asked Treasury officials to produce a costing for the insulation drive on homes that currently have a low energy efficiency rating.
They found that there are currently 13.1 million homes with an energy efficiency rating below C, and upgrading them would be £13 billion a year
Mr Hunt said: “This official costing shows that a key plank of Labour’s policy costs double what they have claimed.
“But given it was all coming out of a £28 billion a year spending splurge which is cancelled one day and then reinstated the next, the overall picture is an opposition party in a general election year that simply does not have an economic plan.
“And when you have an explicit spending commitment without a plan to pay for it, it can only mean one thing – higher taxes.”
Rishi Sunak also took a swipe at Labour’s plans during Prime Minister’s Questions.
He said: “Just this morning, independent Treasury officials have published a formal costing of just one part of their eco-promise – their insulation scheme – and it turns out it will cost double what they previously claimed.
“Not the £6 billion Labour had accounted for but £13 billion pounds every single year. It’s now crystal clear they have absolutely no plan. But we all know how they are going to fund that plan – more taxes on hard working people.”
But a Labour spokesman said: “This costing is ludicrous and uses bogus assumptions. They have costed someone else’s policy, not Labour’s.”
Ms Reeves has vowed there will be “iron discipline” in sticking to Labour’s fiscal rules, including ensuring debt is falling as a percentage of GDP. Other senior figures have also pointedly refused to stand by the green investment plan.
