Gordon Brown yesterday claimed his plans to create a new generation of green jobs would be bigger than Barack Obama's $150bn "Green New Deal", relative to the size of Britain's economy.

In an interview with The Observer yesterday, Brown said he hoped to create 100,000 new jobs over the next few years, many of which he hopes will come as a result of low carbon initiatives.

The prime minister failed to offer specific examples for these new projects, but insisted that the UK "can lead the world in environmental technologies".

"We have new investments being made in wind, wave, solar and obviously nuclear, and then there is the whole question of our homes and our businesses and the extent to which they make the most effective use of energy," he said.

Echoing recent comments from US president-elect Barack Obama, Brown said the global economic downturn could be used as an opportunity to boost investment in green infrastructure projects.

"People will want to use the changes we have got to make as a result of the downturn to take the next step towards building a far more environmentally sustainable economy," he said.

Brown also said that Obama's election victory should "help" deliver an international deal for addressing climate change later this year, but warned that significant challenges remained. "The barrier to an international agreement on carbon emissions is industrialising countries feeling they have not been the historic polluters. We have to get the Chinas and the Indias on board, and that's a big task," he said.

The prime minister's comments came as transport minister Lord Adonis revealed that the government was seriously considering plans for a new £4.5bn high speed rail network, which could feasibly form one of the centre pieces of Brown's Green Newl Deal.

However, in a speech earlier today David Cameron rubbished Brown's claims that the UK had established itself as a genuine leader in the emerging clean tech market, arguing that the government had not done enough to encourage investment in low carbon initiatives.

"Today, British firms have less than a five per cent share of the global market for green goods and services - less than France, Germany, Japan and the United States," he said. "This market is expected to be worth trillions of pounds, and produce millions of new jobs, in the years to come, so we've got to do better - a lot better."

Cameron was speaking at the launch of a new report from the Conservatives outlining the party's policies for encouraging innovation in environmental technologies.

Recommendations include a new stream of funding for clean tech incubator funds, so that every £150,000 of private investment receives up to £600,000 of additional public sector funding, free or heavily subsidised access to facilities where companies can test their product prototypes, and a broader definition of green technology incubators so that any company that delivers an environmental benefit is eligible.