Conservative Party leader David Cameron will today counter criticism that his party has backed away from its commitment to the environment by insisting that green measures make just as much sense in a slowing economy.

In a speech this morning to environmentalists, the Tory leader will say that green policies designed to curb fuel and energy use become more attractive as energy costs rise.

"When oil is moving towards $140 a barrel, when families are being hit hard every time they pay their gas bill, fill up their cars or do the weekly shop, are you telling me we shouldn't – we can't – go green? We've got to. The era of cheap oil is well and truly over."

A Conservative Party spokeswoman said that while some commentators thought green measures became unaffordable when the economy was struggling, the exact opposite was true.

"The cost of living and the strength of the economy can both be helped by the green agenda," she said.

Cameron is expected to propose the wider use of incentives to encourage corporate investment in environmental measures. He will also urge adoption of green taxes – but only where they change behaviour and do not increase the overall tax burden.

The speech comes in the wake of repeated criticism that the Conservatives are backing away from some of the environmental commitments made in the first six months of Cameron's leadership.

In recent months, the party has been vocal in its criticism of many of the government's green tax measures, such as changes to vehicle excise duty and aviation tax.

Speaking last week, environment minister Phil Woolas cited comments from climate change sceptics in the Tory ranks as evidence of the party's "shaky consensus" on global warming.

Cameron will today insist that the party's commitment to curbing carbon emissions remains solid: "We are not going to drop the environmental agenda in an economic downturn."