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David Cameron has praised a new UN deal to curb climate change as a "very significant step forward".

The prime minister said it renewed the international community's determination to tackle carbon emissions through multilateral action.

The agreement, reached in Mexico, includes a fund to help developing countries and a recognition that deeper cuts in carbon emissions are needed.

It is estimated the fund could cost the UK about £1.5bn a year by 2020.

More than 190 countries struck the deal at the latest round of UN climate talks in Cancun, which lasted two weeks.

It had been hoped the agreement would be more comprehensive after last year's meeting in Copenhagen failed to secure a new legally-binding treaty on cutting emissions.

But despite the disappointment, many environmental campaigners say it has thrown a lifeline to efforts to get a deal to tackle climate change back on track.

Energy and Climate Change Secretary Chris Huhne, who was in Cancun, described the deal as a "serious package" of measures.

He acknowledged the agreement did not give everybody everything they wanted and would still require work towards a final deal at a meeting next year in Durban, South Africa.

Mr Cameron congratulated Mr Huhne and the UK team on the "successful conclusion" of the negotiations.

"Now the world must deliver on its promises. There is more hard work to be done ahead of the climate change conference in South Africa next year," he said.

He added that his government would be "greenest ever" and Britain would meet its international obligations.

The government's Climate Change Act prescribes emissions cuts of 80% by 2050 (against a 1990 baseline).

UK emissions are currently 26% below the 1990 level - the baseline year most commonly used in national, European and global policy.

Labour leader Ed Miliband said Cancun had built on the "key provisions of Copenhagen".

"However, there is still a huge amount of work to do to cut global emissions by what the science tell us we need to do," he said.

Ruth Davis, chief policy adviser at Greenpeace UK, said although the progress was limited, the Cancun talks were symbolically important.

"This represents the world's governments coming together to agree that global co-operation is the way to approach this problem, and it was uncertain for quite a lot of the year as to whether we were actually going to get back into that position," she said.

David Norman, director of campaigns at the World Wildlife Fund (WWF), told the 91Èȱ¬ a new global climate change treaty had never been on the cards.

"There was such a disappointment, such a breakdown of trust at Copenhagen last year, this was very much about rebuilding the basis for an agreement," he said.

"We need to go much further. There is a huge gap in ambition between the targets that are on the table now and what will keep us to our stated ambition of keeping global warming rises to 2C."

The "green climate fund" was agreed as part of efforts to channel billions of pounds to poor countries to help them cope with the impacts of global warming and develop without polluting.

Last year's conference in Copenhagen agreed the need to provide $100bn year (£60bn) by 2020 to poor countries to help them cope with the impacts of climate change, such as floods, drought and increasingly severe storms.

Last month, a group of experts including British economist Lord Stern, provided a report for the UN which said finding the £100bn a year would be "challenging but feasible".

Lord Stern, author of the 2006 Stern Review on the cost of tackling global warming, said about half the funding was expected to come from public sources such as carbon taxes while the remainder could come from private investment.

The UK's share of the public money, based on its carbon emissions, would be about 5% of the total, or around £1.5bn a year by 2020.