Niall Ferguson is a professor of history at Harvard University. He is also a senior research fellow at Jesus College, Oxford University, and a senior fellow at the Hoover Institution, Stanford University. His Latest book, Civilization: The West and the Rest, has just been published by Penguin Press.

To listen to some conservative commentary in London on Friday, you would think the British Prime Minister David Cameron just morphed into Winston Churchill, valiantly upholding England’s ancient liberties against German aggression. In fact, what happened in Europe this week was nothing so grandiose.

David Cameron’s refusal to back a Franco-German plan to revise the European Union treaty was the culmination of a consistent Conservative policy, dating back to Margaret Thatcher and continued under John Major. That policy has been to resist any steps taken in the name of European integration that would in practice lead to Britain’s becoming a member of a federal Europe.

Cameron is not—despite the opprobrium that has been heaped on his head by everyone from the French President Nicolas Sarkozy to the shadow foreign secretary Douglas Alexander—a pathologically insular Little Englander. Like Margaret Thatcher, he believes in the single European market. Like John Major, he opposes British membership of the European monetary union. As over the Schengen Agreements on passport-free travel, as over the euro, Britain has once again reserved its right to retain sovereignty over key areas of policy.

Nor is this an exclusively Conservative policy tradition. Gordon Brown, too, resisted the siren calls of the Europhiles in his own party to take Britain into the EMU. I don’t think he did this out of high principle, mind you. I suspect it was partly to spite Tony Blair, partly to maximize the economic power he retained as chancellor of the Exchequer and partly to please his friends in the City, many of whom were rather put off of monetary union by the trauma of Britain’s brief membership of the Exchange Rate Mechanism. Nevertheless, Brown’s preservation of the pound was his single greatest achievement. Had he yielded, the British economy would now be suffering a far more agonizing economic contraction, because we would have lacked the monetary flexibility that was so successfully used by Sir Mervyn King to mitigate the impact of the 2008-9 financial crisis....