Despite his reluctance to mention Europe publicly, the Tory leader showed that in private he was willing to talk extensively to José Manuel Barroso, The Times has learnt. The discussions, at Mr Cameron’s office in the Commons, ranged over how the EU could combat global warming as well as other issues facing Britain.

Mr Barroso, the public face of the Brussels bureaucracy that is detested by many of Mr Cameron’s MPs, said the meeting showed that the issue of climate change rose above domestic politics.

The former Portuguese Prime Minister, who will be in London today for talks on green issues with business leaders, told The Times that the first meeting between the two men was part of a dialogue about “making Europe work”.

The meeting was kept quiet by Mr Cameron’s office because it came shortly after he said that voters had lost faith with the Conservatives in the past because they kept “banging on about Europe”.

Mr Barroso, speaking of last month’s meeting with Mr Cameron, said: “We have spoken about it [the green agenda] and I welcome that because I believe that this commitment to sustainable development and the fight against climate change should not be a classical left-right [issue]. I think that the modern thinking now, be it on the left, the right or the centre, should be committed to these goals.”

Asked whether he was surprised to find Mr Cameron willing to engage with the EU, given his eurosceptic image, Mr Barroso said: “I think that everybody who is reasonable and rational understands that [member states] cannot do it alone. The question today in the 21st century is not to be for or against Europe. It makes no sense. The question is how can we make it work.” He said it was obvious that Britain, Germany or France could not tackle climate change alone.

Mr Cameron’s office yesterday denied that he was changing his position on Europe. A spokesman said: “We have very clear views on what needs to change in the EU — our main thing is that this [Europe] is not an issue that we think should be talked about all the time.”

Mr Barroso also told The Times that he thought nuclear power was a key part of the answer to Europe’s growing energy concerns. While making clear that the choice of energy supply was a matter for member states, he said: “On a personal basis, I believe that nuclear will be more and more on the agenda. When I speak to President Putin, and Russia is among the biggest producers of oil and gas, he told me that his priority is nuclear.

“If you ask my assessment, I have no doubt in telling you that nuclear will be very important and more important in the future than it is today.”

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