Energy Secretary Ed Davey says it will be ‘incredibly difficult’ to govern again with Tories because of their stance on Europe and green policy

The Liberal Democrat energy secretary, Ed Davey, has hinted strongly that he would oppose a second coalition with the Tories because their policy on Europe amounts to “economic and environmental irresponsibility of the highest order”.

Davey, seen as a likely contender in any contest to succeed Nick Clegg, told the Observer that, by contrast, the Lib Dems and Labour shared many views on the environment, although he feared that Ed Miliband’s policy of regulating energy prices would drive away investment.

In a significant intervention in an increasingly tense debate within the Lib Dems, Davey said he found another deal between the Lib Dems and Tories that would involve backing an in/out EU referendum “incredibly difficult” to envisage. The UK had made huge progress in the last five years on green issues and was now a respected international player, but a British government prepared to entertain the idea of leaving the EU would lose influence in climate change negotiations, including crucial talks in Paris at the end of this year.

Davey said: “The Conservative position on Europe is potentially economic and environmental irresponsibility of the highest order. Overall our voice in the debate will be dramatically reduced if at the time we are trying to renegoiate our membership of the EU club before a referendum.”

Some senior Lib Dems believe Clegg would strike a second coalition deal with the Tories after the election, backing legislation to allow an in/out referendum by the end of 2017 in return for major concessions to the Lib Dems, such as progress towards PR in local elections and House of Lords reform.

But senior colleagues, including business secretary Vince Cable, and former party president Tim Farron, also potential leadership contenders, have indicated that they too would find signing up to an EU referendum to be a bridge too far for a pro-European party.

Davey’s intervention adds a “green dimension” to the argument. He pointed out that his party would be putting its commitment to a low-carbon economy on the front of its election manifesto, and suggested this would sit uneasily with any deal with the Tories which involved a potential EU exit. “I am genuinely worried,” he said. “The Tories are putting the national interest behind the party interest. It will be very difficult to get Liberal Democrat agreement to an EU referendum.”