Gordon Brown tonight led a chorus of condemnation against "flat-earth" climate change sceptics who have tried to derail the Copenhagen summit by casting doubt on the evidence for global warming.

Sceptics in the UK and the US have moved to capitalise on a series of hacked emails from climate change scientists at the University of East Anglia, claiming they show attempts to hide information that does not support the case for human activity causing rising temperatures.

On the eve of the Copenhagen summit, Saudi Arabia and Republican members of the US Congress have used the emails to claim the need for urgent action to cut carbon emissions has been undermined.

But tonight the prime minister, his environment secretary, Ed Miliband, and Ed Markey, the man who co-authored the US climate change bill, joined forces to condemn the sceptics.

"With only days to go before Copenhagen we mustn't be distracted by the behind-the-times, anti-science, flat-earth climate sceptics," Brown told the Guardian. "We know the science. We know what we must do. We must now act and close the 5bn-tonne gap. That will seal the deal."

According to the government adviser Sir Nicholas Stern, 10bn tonnes of greenhouse gas emissions must be taken out of the atmosphere by 2020. So far agreement is in place for only half of that amount.

Ed Miliband gave his most damning assessment of the sceptics yet, describing them as "dangerous and deceitful".

He said: "The approach of the climate saboteurs is to misuse data and mislead people. The sceptics are playing politics with science in a dangerous and deceitful manner. There is no easy way out of tackling climate change despite what they would have us believe. The evidence is clear and the time we have to act is short. To abandon this process now would lead to misery and catastrophe for millions."

Markey warned against allowing America's political agenda to be hijacked by the email affair. "We can no longer allow our climate and energy policy to be hijacked by the government of Saudi Arabia, ExxonMobil, and the defenders of the fossil fuel status quo," he said.

Even if an investigation into the university emails were to show evidence of wrongdoing, scientists and politicians say there is an overwhelming body of evidence that humans are causing climate change. However, the hacking affair is putting new obstacles in the way of getting a bill past Congress – seen as a crucial precondition for a binding climate change treaty.

The summit, which begins on Monday, aims to seal a global deal to control greenhouse gas emissions, but all of the significant issues remain to be resolved. There is still no agreement between developing nations and the richer countries over the carbon cuts required and the funding which must be given to poorer countries to help them cope with global warming.

China and India, whose economies are growing rapidly, must still agree a deal on curbing their emissions while being able to lift billions of people out of poverty.

The concern for some of those attempting to drive through a global deal is that the sceptics will delay critical decisions by casting doubt over the science at a time when momentum has been gathering towards a historic agreement. "The sceptics have clearly seized upon this as an incident that they can use to their own ends in trying to disrupt the Copenhagen agreements," said Bob Watson, Defra chief scientist and former head of the Intergovernmental Panel on Climate Change. "If this slows down an international agreement to significantly reduce greenhouse gases, it will mean we're committed to an even larger temperature change … with adverse consequences on agriculture, water, human security, human health and biodiversity."

Nick Clegg, the Lib Dem leader, said it would be disastrous for the planet if sceptics were able to undermine support for a climate change deal. "Ideological dinosaurs, whether in Saudi Arabia or in the Conservative party, who deny climate change must not be allowed to hide behind some leaked correspondence to support their outdated theories," Clegg said.

A number of prominent Conservatives, including former chancellor Lord Lawson and former Cameron frontbencher David Davis, have pounced on the email furore. But tonight the shadow climate change secretary, Greg Clark, made clear the party line remains that climate change is a serious man-made threat. "Research into climate change has involved thousands of different scientists, pursuing many separate lines of independent inquiry over many years. The case for a global deal is still strong and in many aspects, such as the daily destruction of the Earth's rainforests, desperately urgent," he said.

Additional reporting by Alok Jha and Andrew Sparrow