Britain faces a catastrophic future of deadly heatwaves, floods and droughts if efforts to secure a new global climate change deal fail, Gordon Brown will warn today.

In a bleak message to representatives of 17 leading nations, who have gathered in London in advance of the UN-sponsored climate summit in Copenhagen in December, Mr Brown will say that there is “no plan B” if negotiators fail to reach a deal.

With fewer than 50 days to go until the summit, concerns remain that international wrangles over emission cuts’ targets will end in deadlock.

Mr Brown, who has pledged to attend the summit in person, will renew his call to fellow world leaders to speed up efforts to iron out their differences. “If we do not reach a deal at this time, let us be in no doubt: once the damage from unchecked emissions growth is done, no retrospective global agreement, in some future period, can undo that choice,” he will tell the Major Economies Forum.

The Prime Minister will say that by 2080 an extra 1.8 billion people — a quarter of the world’s current population — could lack sufficient water. Making a reference to the summer heatwave of 2003 in Europe, which led to more than 35,000 extra deaths, he will say: “Such an event could become quite routine in Britain in just a few decades’ time”.

Agreement at Copenhagen “is possible”, he will add. “But we must frankly face the plain fact that our negotiators are not getting to agreement quickly enough. So I believe that leaders must engage directly to break the impasse.

“If we falter, the Earth itself will be at risk . . . For the planet, there is no plan B.”

Meanwhile, more than 1,000 climate change demonstrators clashed with police beside a coal-fired power station in Nottinghamshire. Police said that there had been 52 arrests by midmorning yesterday. They admitted that some protesters had been bitten by police dogs and suffered other injuries as they tried to tear up perimeter fencing. Chief Inspector Linda McCarthy, of Nottinghamshire Police, said: “Of course this is regrettable, but it’s a combination of reckless behaviour by some of the protesters and us having to respond with a different style of policing.”

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