Philippe Naughton and Ben Webster in Copenhagen
Gordon Brown has brought forward his arrival in Copenhagen to tomorrow night in order to be seen to be the first major world leader to join the climate summit.
Ed Miliband, the Climate Change Secretary, said that the Prime Minister hoped to inject a note of urgency into negotiations towards a new global climate pact.
"I think that it's a sign of the seriousness with which he takes this issue and I think it's a sign that the negotiations are moving too slowly," Mr Miliband told a press conference in Copenhagen. "My very clear feeling is that ministers and negotiators need to start getting their act together."
Many of the 120 national leaders due to attend the summit have also brought forward their arrival dates and about 20 will be arriving on Wednesday morning. Mr Brown is keen to give the impression that he is more engaged than any other leader in striking a global deal on greenhouse gas emissions.
With speculation rife that he will call a snap election early in the new year, Downing Street will be hoping to use the Copenhagen summit to burnish the Prime Minister's image as a world statesman, especially if he can help to engineer a meaningful accord to tackle global warming.
Mr Brown is not expected to join the negotiations until Wednesday, by when a succession of developing country leaders will be making "national statements" in a plenary session of the conference.
Behind the scenes and in less formal working groups, negotiators will be working around the clock drafting and redrafting paragraphs in the negotiating texts, ready for the leaders to make the hard political decisions on carbon dioxide emissions targets and long-term financing.
The obstacles to an agreement are still significant, especially between the two key players, the United States and China, which together account for around 40 per cent of global carbon dioxide emissions.
The US is the world's largest per capita CO2 emitter but walked away from the Kyoto Protocol eight years ago, making it the only major developed nation exempt from the obligations of that treaty. President Obama continues to reject Kyoto, but has made a firm, albeit unambitious, offer to start cutting US emissions over the next decade.
China overtook the United States as the world's biggest emitter of carbon dioxide two years ago but rejects the notion that it, too, will have to join a binding emissions reduction regime. Despite its export-led industrial success, China insists that economic development must remain its priority.
The competing demands of these two global powers means that the European nations are effectively sidelined in the negotiations that matter. The EU wants developed countries to reduce their CO2 emissions by 30 per cent by 2020, far beyond what the Americans are currently willing to accept.
The situation is complicated by the fact that there are two separate tracks in the negotiations — for an extension of the Kyoto Protocol with another round of binding emissions targets, and for an entirely new agreement bringing in the Americans.
The Japanese, who hosted the Kyoto meeting 12 years ago, threatened last week to walk away from that agreement if there is no significant progress on a new treaty, and there have been calls for Europe to do the same and to renew the push at a later date.
But Mr Miliband said that the Copenhagen summit was still the best chance to tackle the problem. "This is not just about getting any old deal and it is really important to say that," he said. "I don't think that Plan B is a good option at all. In other words, putting it off is not the answer. This is not going to get any easier."
He said that Mr Obama's election and the growing international consensus on the risks posed by global warming meant that "the stars are aligned that make this the most the most propitious time for a new agreement".
In talks last Friday, EU leaders agreed to commit £6.5 billion to a new "fast track" financing fund for Third World nations most vulnerable to rising temperatures. That fund is expected to hand out $10 billion (£6.1 billion) a year for the next three years, but the longer-term funding — which the UK puts at $100 billion a year by 2020 — has yet to be found.
Small island states and sub-Saharan African nations have called for the summit to endorse a target for the rise in global average temperatures to be limited to 1.5C, more ambitious than the 2C target proposed by Europe.
A negotiating text circulated on Friday did not fix a clear target on what is known as "global peaking" — the idea that worldwide emissions will start to have to fall by a certain date if the world is to have any chance of averting catastrophic warming.
Mr Milliband said that emissions had to peak by 2020, although developing countries' emissions might continue to rise past that point. "We're not asking developing countries to necessarily peak by 2020 but we need a global peak," he said. "Unless we get global peaking by, at the latest, 2020, then we're going to find that we have runaway climate change. All the science tells us that.