Cameron under pressure: When it comes to the EU, his party is increasingly ungovernable.

Everything you need to know about the Tory EU rebellion in five minutes

Everything you need to know about the Tory EU rebellion in five minutes

In a day or two, Tory MPs will vote against their own Queen's Speech in order to attach a symbolic statement reiterating what their leader has already promised them. It's all very baffling. What exactly are they trying to achieve and how much damage will it cause David Cameron?

What are Tory backbenchers doing?

Leading Conservative eurosceptics have tabled an amendment to the motion welcoming the Queen's Speech. At the end of line five, they want to add the statement: "But respectfully regret that an EU referendum bill was not included in the Gracious Speech".

The effort is led by one of parliament's most die-hard eurosceptics, John Baron, with able assistance by fellow right-wing troublemaker Peter Bone. Most of the other signatories are the usual suspects: bad tempered Tory backbenchers who are now quite used to rocking the boat. In fact, it's almost second nature. They include: Philip Hollobone, Philip Davies, Douglas Carswell, David Davis, Nick de Bois, Adam Afriyie, Zac Goldsmith, John Redwood and Aidan Burley.

The amendment is highly unlikely to succeed, because Liberal Democrats, Labour and many Tory MPs will vote against it or abstain.

What will the amendment achieve?

The amendment will achieve nothing. It is pure theatre, an entirely symbolic act stating their protest at the lack of a bill on an EU referendum in this year's legislative agenda. David Cameron has already promised a referendum in 2017/18 if he wins the general election. Under his plans he would secure a new deal on British membership of the EU first and then put the package to the British people.

Rebel Tories are trying to build pressure for Cameron to pass a bill in this parliament ensuring a referendum in the next parliament. The best way to do this is with a show of strength: dozens of Tory MPs showing they are prepared to stand firm on the subject. Evidently, they don't trust Cameron's promise.

How is Cameron reacting?

Downing Street learned some lessons from its Commons defeats last year. This time round they have been careful to stress how comfortable they are with the amendment, so that a big wave of support for it is not interpreted as a challenge to Cameron's leadership. Unfortunately, this puts the prime minister in the strange position of acting comfortable with the idea of a large section of his own party voting against his own legislative agenda for the year ahead.

The middle path pursued by Downing Street is that ministers will be forced to abstain, while MPs can vote how they like. A whipped abstention is a strange parliamentary manoeuvre, but then the entire situation is highly unusual.

Parliamentary private secretaries (PPS) will be allowed a free vote. This is a smart move by No.10. When they tried to control them for previous rebellions, the PPS' decision to step down provided a steady drip of martyrs for the media to fixate on in the run-up to the vote.

Cameron himself is in the US until Thursday, meaning he will miss the vote if it is held, as seems likely, on Tuesday or Wednesday.

But what does this do to the prime minister's authority?

Leave it in tatters. Tory MP Gavin Barwell told the BBC he trusted the prime minister but that the voters no longer trust politicians in general and that therefore legislation cementing a promise was reasonable. That isn't the message voters will get from the manoeuvre. Instead, they will ask: If his own MPs don't trust him, why should the electorate?

By attaching the amendment to the Queen's Speech, the rebels are being particularly brutal. It looked at one point like the move could even force Cameron to resign. According to parliamentary convention, prime ministers must resign if the Queen's Speech or Budget is amended. The last time this happened was in 1924, when Stanley Baldwin was forced to step down and the first Labour government was formed under Ramsey MacDonald. However, since the Fixed-Term Parliament Act, no confidence votes in the government must take the form of a motion starting: 'That this House has no confidence in Her Majesty's government.' Budgets and Queen's Speech amendments no longer count.

The worst aspect, from Cameron's perspective, is that this comes just as things were looking up for him. After the death of Margaret Thatcher he was enjoying a moment of rare discipline in the party. New organisational changes at the top brought in more questioning MPs for a role in policy formation. Everything was getting quite touchy-feely. New Labour grandees were attacking Ed Miliband. It seemed, for a couple of weeks, as if perhaps the Tories were coming out of a mid-term slump. Now, with just two years left until the general election, the party looks as divided as it ever has.

What does this do to Tory prospects at the next election?

Hurt them. The Tories are, in the words of Cameron himself, back to "banging on about Europe". While it's true that the public generally agrees with them, voters put Europe usually at about number five in their list of concerns – a very long way down from the economy. But with no signs of an economic recovery on the horizon, Tory MPs are spending their entire time talking about the EU.

Furthermore, sabotaging their own leader's Queen's Speech is as strong an indication of fratricide as a party could accomplish. And typically, voters reject divided parties.

"[Tabling the amendment] is not just foolish, it is quite contrary to all the political instincts of a responsible political party that wants to hold and retain power after the next general election," former foreign secretary Malcolm Rifkind told the BBC. "This amendment isn’t going to get carried. So all those supporting it will have achieved is they will have split their own party, they will cast questions over the prime minister’s authority, and indirectly, unintentionally, they will be helping the Labour party’s prospects at the next election."

Tories are also likely to table backbench bills demanding a referendum on the EU or amend relevant legislation going through the House. This isn't the end of Cameron's troubles. It's probably just the start.

Nor is it just the EU. As the Conservative parliamentary party becomes more comfortable with rebellions, it breaks ranks on all number of things. The most recent example is of support from 150 Tory MPs for a referendum on gay marriage.

Is the Tory party split on Europe once again?

Yes, but not in the way you might expect. Previous Tory governments were torn apart by the split between europhiles like Ken Clarke and eurosceptics, like, well, the rest of them. That split no longer exists. EU supporters like Clarke or new Conservative policy chief Jo Johnson are few in number. Almost the entirety of the Tory party is eurosceptic.

Instead, the divide is between those who want to leave (preferably immediately) and those who want to renegotiate terms. Cameron and most (but not all) of the party leadership are in the latter camp. They are eurosceptic, but their demands are more for distance than divorce. They want to challenge the idea that power transfers can only ever go towards Brussels.

Most Tories want out. Nigel Lawson was the first party grandee to break ranks and say he would vote to leave no matter what deal Cameron stitches together in Brussels. He was followed by Norman Lamont and Michael Portillo. The current crop of active Tory politicians has not ruled out voting 'in', but they have started to make it perfectly clear how unlikely they are to do so. Education secretary Michael Gove, defence secretary Phillip Hammond and London mayor Boris Johnson have said Cameron should have a chance to renegotiate powers before they make their mind up – but that if the vote happened now they would vote 'out'.

Or, as Boris so succinctly put it: "He has my full support, and I personally back legislation now to make sure that referendum goes ahead."

What happens next?

The amendment will be defeated but the sense of a Tory party in disarray will persist. Backbench legislation will be introduced calling for a referendum in the next parliament, or it will appear as an amendment to existing bills. Cameron will probably be able to fight it off, but the amount of damage he takes while doing so will demonstrate one of the most reliable rules in current British politics: Ed Miliband is a very fortunate opposition leader. The Tories are effectively ungovernable.