Ken Clarke has stepped up the pro-European rhetoric as the battle over Britain's future in the EU intensifies, warning that a referendum on the issue is a "gamble" and that David Cameron may be about to open the door accidentally to a British exit.
Although the veteran Tory minister and the cabinet's leading pro-European insists the argument for Britain taking a leading role in Europe can be won, he fears a referendum could be used as a vehicle for protest against an unpopular government.
Mr Cameron is expected to use a speech in the Netherlands on Friday to announce plans to renegotiate Britain's status in the EU – if he wins the next election – and to seek the "fresh consent" of the British people in a referendum.
But the former chancellor – who attends cabinet in a roving ministerial role spanning growth, national security and trade – believes any referendum would be several years away and that voters could use it to punish an unpopular midterm government.
"Europe is not the primary interest of the British public and all kinds of things can arouse protest," the veteran minister said in an interview with the Financial Times.
Pro-European countries such as Ireland and France had voted No in EU referendums as "a protest against unpopular governments or about economic difficulties", he said.
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While many younger pro-European Tory MPs refuse to speak publicly on the issue for fear of upsetting their local party activists, Mr Clarke turned his fire on the "30 or 40 Conservative MPs" he claims want to leave the EU.
He compared them to Tory enthusiasts for capital punishment during the 1970s, who only backed a referendum on the issue because they knew they could not command a majority in parliament.
"If you realize you're doomed in parliament you demand a referendum – that's what the hangers and floggers used to do," he said.
Mr Clarke's ardent pro-Europeanism is deemed by his critics to belong to another age; they argue that his longstanding opposition to a referendum is typical of an elite that does not want to expose its views to a public vote.
However he believes a referendum is inevitable and is supporting a new cross-party think-tank – including Labour former minister Lord Mandelson – to make the case for full engagement in the EU.
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Mr Clarke admits that pro-Europeans have effectively abandoned the battlefield and need to regroup quickly. "All referenda are a bit of a gamble. I don't think we can take a Yes vote for granted," he said.
"I think one of the problems is, because so much of the media is overwhelmingly eurosceptic, no one has really campaigned very vigorously for the case for British leadership in the European Union for probably a decade or more."
Mr Clarke argues that Britain should play a leading role in Europe on issues such as trade, the single market and foreign policy and that his party should not undermine its case by making ill-conceived lists of policies they want to repatriate from Brussels.
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"I think if Britain ever does leave the European Union it will be difficult to adjust to our loss of a leading role in the political evolution of Europe and our reduced role in the global political world," he said.
Mr Cameron will on Wednesday brief Tory cabinet ministers on the contents of his Europe speech, whose most controversial elements will only apply after 2015 if the Tories win the election. Nick Clegg, his Liberal Democrat deputy, will be given a copy nearer the time of the speech's delivery.
The prime minister is also ringing fellow European leaders to explain the background to the speech, hoping to smooth ruffled feathers and reassure them that – whatever they might read in the UK press – he remains committed to Britain's EU membership.