“Blackmail,” as countless on-screen villains have observed over the decades, “is such an ugly word.” And, if you want to understand how an ostensibly small group of Tory Euro-fanatics has exercised such a hold over their leaders for so long, it’s probably not the most accurate one. Extortion – getting what you want, not by threatening to reveal something about someone but by threatening to hurt them in some way – is more accurate.

Sometimes that threat is as obvious as it’s effective, namely to deny a Conservative prime minister in possession of a small or non-existent parliamentary majority the votes he or she needs to get something through the House of Commons. Theresa May is hardly first of her ilk to know how that feels.

John Major might have snatched victory from the jaws of defeat at the 1992 general election. But his overall majority fell to just 21. That proved nowhere near enough to outweigh the admittedly small minority of backbenchers who’d convinced themselves, first, that Margaret Thatcher had been stabbed in the back by a cabinet cabal of Europhiles in 1990 and, second, that the UK’s ignominious exit from the ERM two years later was proof positive that nothing good could come out of Europe, either for the country or the party.

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Other times, the threat is as much extra-parliamentary as it is legislative – namely, the suggestion that, without the support of the Euro-fanatics, a would-be leader won’t make it to the top in the first place. Back in 2016, May clearly felt, as a remainer (albeit a very reluctant one), she had to do everything she could to match the zeal of the leave campaigners she needed to beat. But, again, that was nothing new.

David Cameron may have been Michael Howard’s choice as his successor in 2005 after he’d presided over the party’s third election defeat on the trot, but Cameron wasn’t the starting favourite. And he was well aware that, four years previously, the candidate who should have won hands-down (Ken Clarke) was beaten by a total inadequate (Iain Duncan Smith) solely because one was Eurosceptic and the other wasn’t. So when Liam Fox promised to pull Tory MEPs out of the European People’s party-European Democrats (EPP-ED) group in the European parliament, Cameron (unlike, note, David Davis) positively (but almost certainly unnecessarily) rushed to follow suit.

Once that initial dependence is established, it then becomes impossible, both psychologically and practically, to throw off. May must know this now – but Cameron’s experience could have told her from the get-go. His fear of the party’s Euro-fanatics grew with every passing year, especially once he was forced, after the Lisbon treaty was ratified, to abandon his “cast-iron” pledge to put it to a people’s vote – not a good look, particularly when Ukip could plausibly claim to have denied the Tories a far more convincing win at the 2009 European parliament elections.

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In opposition, Cameron’s fearful dependence led to his promising the repatriation of policies and a “referendum lock” on further transfers of power to Brussels. True, along with Nigel Farage giving up the leadership so as to focus on yet another doomed attempt to win a Commons seat, as well as the inexorable logic of our first-past-the-post electoral system, that promise may have helped put Ukip temporarily back in its box at the 2010 general election. But not firmly enough to prevent the myth taking hold among Tory activists, candidates and MPs that Ukip, by winning more votes than the margin of victory obtained by Labour and Liberal Democrat MPs in some constituencies, had denied the Conservatives an outright victory.

In the government, and in the light of more than 20 Tory rebellions against the Lib-Con coalition on Europe (including one in October 2011 in which as many as 81 Conservative MPs voted for a full-blown in-out referendum), that same fearful dependence then led Cameron to veto the EU’s treaty-based response to the eurozone crisis – a move that, after gaining him a hero’s welcome back in the Commons, soon backfired when it became obvious that the other member states could go ahead anyway.

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And then, of course, came Cameron’s fateful promise, in his Bloomberg speech in January 2013, to hold a vote on the UK’s EU membership – a move intended, perhaps paradoxically, to face down the party’s Euro-fanatics in the long-term by appeasing them in the short, as well as to supposedly shoot Ukip’s fox. Sadly, and some would say predictably, it failed miserably – just as the attempts of the then home secretary, May, to bang on about immigration failed miserably, too. The rest, as they say, is history.

No one, then, should allow the recent failure of Messrs Rees-Mogg and Baker to muster the famous 48 letters required to trigger a no-confidence vote in May to fool them into thinking that Conservative Euro-fanatics are and always have been merely a phantom army. Sure, maybe once upon a time that was the case, and maybe they’ve never been quite as numerous as they, and their equally obsessive media cheerleaders, have liked to suggest. But, with the Tory press (and indeed ConHome) on their side, with Ukip waiting in the wings, with constituency associations and even their less fanatical parliamentary colleagues growing ever more hostile to the EU, and – most importantly – with the maths as tight as it’s often been, they haven’t really needed to be. And that remains as true right now as it has been in the past.

• Tim Bale is professor of politics at Queen Mary University of London