Britain will face a disaster if it adopts an “isolationist approach” to the environment, the energy secretary, Ed Davey, has warned as he announced the UK is to give £720m to an international fund to help poor countries cope with climate change.

In remarks aimed at rightwing Tories and Ukip supporters, as voters go to the polls in the Rochester and Strood byelection, Davey said a “little Englander approach” would be self defeating as climate change does not recognise borders.

Davey was speaking to the Guardian on the eve of an announcement that Britain is to donate more than France and Germany to the UN’s Green Climate Fund which has a target of $10bn (£8bn). The UK commitment to the fund, seen as a vital step towards rich and poor nations sealing a deal to tackle global warming in 2015, is surpassed only by the US and Japan.

The enthusiasm with which Davey has announced the UK contribution contrasts with reticence in Downing Street, where David Cameron is understood to be nervous about highlighting Britain’s contribution to tackling climate change as it faces the prospect of losing its second parliamentary seat to Ukip. The prime minister was at pains to point out at the recent G20 summit in Australia that the UK’s £720m contribution is not new money.

Davey said the prime minister should be more robust in challenging climate change sceptics on the Tory right, such as the former environment secretary Owen Paterson, and Ukip suporters.

The energy and climate change secretary told the Guardian: “A little Englander approach, an isolationist approach, is going to be a disaster for the people of Britain. Climate change does not recognise borders.” Experts warned recently that global warming would affect health, business and food production in the UK, with a senior military figure also warning that armed forces would be unable to provide global security if climate change goes unchecked. “There is a huge amount at stake,” said Davey. “Anyone who has followed the UN negotiations knows the poorest and most vulnerable countries on the planet are looking to developed countries to help them survive climate change. If we do not do this, I don’t think we will get a global deal. It is as simple as that.”

He said: “[Critics] do not realise the vital work this money is for. This is about saving lives and we have duty to do this.” Examples, he said, were helping low-lying nations cope with rising sea levels and subsistence farmers cope with failing crops. The contribution to the GCF will come from an existing UK climate aid fund that will spend £3.9bn from 2011-16.

Asked why the UK was offering the equivalent of $1.13bn, more than the $1bn pledged each by Germany and France, Davey said the UK would only pay the extra if other countries came forward to contribute. “We are doing that to encourage others to give,” he said. So far, 14 other nations including Mexico and South Korea have contributed to the GCF, bringing the total with the UK contribution to about $9bn. Australia, led by climate sceptic Tony Abbott, has refused to give money to the ECF.

Davey said that the recent agreement of EU leaders to cut greenhouse gas emissions by 40% by 2030 provided a chance to reject the politics of division. He said: “In the UK, we may be experiencing the politics of division – whether from the Scottish Nationalists or Ukip. And our TV screens may be full of conflicts from Syria to Ukraine. Yet, remarkably, climate politics is experiencing a quiet but steady recognition of our common goals and shared interests.