Some Conservative MPs are great defenders of the sovereignty of parliaments.

Of their parliament, at any rate. They bridle at the injustice of being subjugated, as they see it, to decisions made in distant capitals. Irony is not their strong suit.

They are very serious, nevertheless, about the collection of grievances they call "Europe". One after the other, Tory leaders have had to live with the fact. Their party contains a group that would be happy enough with a European free trade area. Anything else, anything called a union, and any union to which the words "ever closer" can be attached, is anathema.

Over the weekend, 50 of these unreconciled UK nationalists identified themselves as Conservatives for Britain. Former ministers John Redwood and Owen Paterson are among their number. Their co-chairman, Steve Baker, MP for Wycombe, predicted in a TV interview that at least another 50 backbenchers would declare themselves in due course. The aim, scarcely veiled, is to cause a great deal of trouble for David Cameron.

He has enough of that to be going on with, some of it of his own making. Several Cabinet ministers, notably (predictably) Iain Duncan Smith, are anything but averse to the Conservatives for Britain programme. The latest Tory intake is as eurosceptic as any. The Prime Minister has meanwhile been making the kind of mistakes usually associated with panic. These are not happy times for a newly-triumphant government.

Tory euroscepticism is a strange phenomenon. A party truly ruthless in its pursuit of power would have no truck with an obsession that, time and again, has destroyed its unity and shattered its credibility. Mr Duncan Smith's stint as a hapless, hopeless leader should be warning enough. As things stand, withdrawal from the European Union lacks public support and the Tories have a slim Commons majority. It's not the ideal moment for a squabble.

Mr Cameron certainly knows as much. Early in his leadership he hoped somehow to avoid the issue of Europe, but then painted himself into a corner with the broken promise of a referendum. Held to his word finally, in January 2013, he finds himself submitting a few arguments over EU reform to a plebiscite over the UK's very membership of the European project. From a bad, temporising start, the Prime Minister has proceeded to make matters worse.

He was unlucky, it turns out, to win the General Election. Stripped of the shield of coalition, Mr Cameron must confront his own party. He has stumbled, meanwhile, over the concept of collective Cabinet responsibility. Will ministers be sacked if they refuse to toe his line? That's what the Prime Minister seemed to say in January. Now Downing Street says obedience will only be expected while Mr Cameron "renegotiates" the UK-EU relationship. A decision on what follows has supposedly not been made. That position is unsustainable.

Next year or the year after, when real arguments begin, the sight and sound of colleagues at each other's throats will fail to impress many voters. This is not 1975 and Mr Cameron is not Harold Wilson. The Tories will not patch up differences afterwards, as Labour did 40 years back, as though nothing important has happened. For the sceptics, Europe is the central political issue of the age. The wounds from a referendum will be raw for a generation.

Mr Cameron is trapped in that reality, yet still he pretends otherwise. Yesterday, the European Union (Referendum) Bill received its second reading. In one way, it was a formality, a simple matter of agreeing on the mechanics of the vote. But the Government's decision to scrap the rules on Whitehall non-intervention ("purdah") before the referendum suggests Mr Cameron will use all means to get his way. Given what went on before Scotland's vote, it counts as refreshing honesty. But it is not a sign of confidence.

The confusion over the role of ministers has already irritated many in his party. The purdah decision will alienate a few more. If Mr Baker is right, meanwhile - and few doubt it - at least one third of Tory MPs are ready to demand things of Mr Cameron that he cannot or will not deliver, no matter how loudly he proclaims his personal VE Day. The "repatriation of sovereignty" - effectively, the right to ignore EU legislation - is tantamount to tearing up the European Communities Act 1972. Sceptics hardly bother to deny it.

At this point, those who did not care to vote Tory on May 7, all 19.35 million of them, might wonder why a great issue of the day has already begun to be treated as the private business of a party sect. If recent surveys are correct, it is not even a cult that has the slightest right to speak "for Britain" on the subject of the EU. And as Nicola Sturgeon never tires of pointing out, the advertised virtues of the UK mean that any decision cannot in fairness be a purely English, far less Tory, matter.

The sceptics don't care about that. They want Mr Cameron to trot off to Europe and they want to see him fail. Such are their demands he cannot, in their terms, hope to succeed. For Mr Baker and his friends, that's close to ideal. A majority of British voters might want to stick with the EU, but the entire purpose of Conservatives "for Britain" is to remind Mr Cameron of parliamentary arithmetic and force him into ever more obdurate negotiating positions.

It's hardly a clever, or even rational, use of a Commons majority. Fixated on their obsession, the sceptics can't see it. You could say - now where did this expression arise? - that they are threatening to "hold the Government to ransom" if its attitude towards Europe does not suit their comic book. Instead, they will deliver him to the mercies of rival parties.

The sceptics mean to play hard-ball in their efforts to force Britain from the EU? They mean to remind the Prime Minister that his majority is fragile? Do they imagine they are the only bloc of MPs to have noticed the fact? If Conservatives for Britain mean to push Mr Cameron into the corner once occupied by John Major, they will leave him relying on Labour and the Scottish National Party in Commons arguments. Smart move.

Sceptics can campaign, honourably or not, for an "out" vote, or they can wreck their party. To do both would be worse than careless, at least in the eyes of people who voted Tory. If the "out" campaign leaves the Prime Minister beholden to Labour and the SNP, it would mean one thing: the EU obsession counts for more among the true believers than party or country. The fact that this happens to be true, that only "out" will ever do for hard-core sceptics, invites the voters' judgment.

There's a lesson in all of this. Those who crow that the SNP - for example - have no power to do X, Y, or Z still do not grasp the plain fact. Mr Cameron is a prime minister condemned to weakness for the next five years. Europe is the big story, but it is not the only story.