US President Barack Obama is joining world leaders in Copenhagen in a final push to secure a new deal on climate change amid growing optimism that an agreement can be reached.
The deadlocked talks had previously been boosted by a US announcement that it would back proposals for 100 billion dollars-a-year (£62 billion) of long-term international funding to help developing countries in the fight against global warming.
And there were suggestions at the UN climate summit in the Danish capital that Mr Obama would announce an increase in the level of emissions cuts the US could make by 2020, to seal the deal.
For days the talks had been mired in procedural wrangling, preventing negotiators from getting to grips with key issues of emissions cuts, transparency on the actions nations were taking and financial and technological support for the poorest parts of the world to cope with climate change.
But Prime Minister Gordon Brown said the conditions for a global climate deal were now in place after breakthroughs at the summit.
Mr Brown said the new finance offer from the US meant the UN summit was "absolutely" more than halfway to securing agreement although talks are continuing.
And he confirmed that the next scheduled global warming conference, due to be held in Mexico late next year, could be brought forward to the summer to speed progress towards a legally-binding deal.
Almost 120 leaders are attending the last scheduled day of the Copenhagen talks, which it is hoped will result in a political accord that can be turned into a legal treaty within the next year.
The more upbeat mood among British politicians attending the summit came after the news Washington was "prepared to work with other countries toward a goal of jointly mobilising" the 100 billion dollar-a-year fund, if a "strong accord" was agreed.
US Secretary of State Hillary Clinton said the conditions of the financial package included "all major economies stand behind meaningful mitigation actions and provide full transparency as to their implementation", sending a clear message to the Chinese that the issue of transparency was a potential deal-breaker.