Ed Davey accused the Tories of “clinging to fossil” as he tried to woo eco-friendly Blue Wall voters.
The Liberal Democrat leader was set to use his first autumn party conference speech to take a swipe at Rishi Sunak after the Prime Minister rolled back on key green pledges.
Mr Sunak last week pushed back the deadline for selling new petrol and diesel cars and delayed the phasing out of gas boilers
Sir Ed was expected to say: “Britain led the world, and we can lead it again.
“But not with the Conservatives squabbling amongst themselves and clinging to the fossil fuels of the past.
“And not with the Prime Minister refusing even to attend the United Nations General Assembly last week.
“Instead of standing at his lectern in Downing Street single-handedly trashing our economic future,
“Rishi Sunak should have been in New York working with global leaders to tackle this crisis together.
“Our vision is for a Britain that leads the world as we embrace the economy of the future.
“The Conservatives would only shackle us to the past.”
The Lib Dems have used their party conference in Bournemouth to lay out policies appealing to traditionally Tory voters, predominantly in the south east.
Sir Ed yesterday ruled out his party seeking tax rises on even the richest workers as he targeted disaffected Conservative voters.
However last night members defied the party leadership by voting to keep the Lib Dem housebuilding target for England.
Sir Ed had wanted to shelve a 380,000 annual homes target, arguing it had failed to deliver the houses people wanted.
But following a lively debate members backed a motion from younger activists to keep it after the they warned dropping the target would hand Labour “a stick to beat us with” in marginal seats.