Leading article: Experiment in pluralism may have run its course

The anger of senior Liberal Democrats following on from David Cameron's flawed diplomacy at last week's EU summit becomes more intense and vocal. On Friday the party's leader, Nick Clegg, appeared gullibly supportive of Mr Cameron's actions, choosing instead to lay the entire blame for Britain's veto of a new eurozone deal on President Nicolas Sarkozy of France alone.

It was a reaction that appeared weak and unconvincing – at the very least conveying the impression that Mr Clegg was willing to accept almost any departure from deeply held convictions in order to sustain the Coalition. Fortunately, over the weekend senior Lib Dem figures have been less restrained, and Mr Clegg himself has found something closer to his true voice. Among the most telling words were those of the former Lib Dem leader, Lord Ashdown. "We have isolated ourselves from Europe and diminished ourselves," he said.

Meanwhile, David Owen, writing in The Independent today, refers to Mr Cameron's "serious miscalculation" and warns of a "chasm" opening up in the Coalition. His one-time SDP partner Shirley Williams believes that what has happened is "a massive defeat for Britain in Washington, Beijing, New Delhi – capitals that value the influence they believe we have in Brussels".

We have reached a pivotal moment in the short history of the Tory-Liberal-Democrat Coalition, with a devoutly pro-European party propping up a Conservative Prime Minister who appears to have voluntarily excluded Britain from vital decision-making in the EU, a mind-boggling contortion.

The more that Mr Cameron insists that he made only modest demands of his European colleagues, the more urgently the question is raised about why, if those demands were so modest, they obtained no support from any other EU members. Mr Sarkozy and Angela Merkel are two leaders on the centre-right, like the British Prime Minister, and yet they evidently felt no inclination to help him. This raises a number of other questions, first about whether this isolation is part of the price being paid for Mr Cameron's previously disdainful attitude to Europe, and also about whether Mr Cameron is being held hostage by his party's Eurosceptics . Has he simply revealed his true colours – recklessly wielding a British veto without thinking of the consequences?

For the Liberal Democrats, this is cause for serious reflection. They have already failed to secure electoral reform from being in the Coalition. They suffer in the polls for spending decisions that the two parties have taken in Government. They are tied into the contentious economic policies of the Chancellor, George Osborne, for two years beyond the next election. Now they find themselves sustaining Mr Cameron's diplomacy in Europe that in terms of euroscepticism goes well beyond any act of hostility that Margaret Thatcher attempted.

With good cause, Mr Clegg and his party are passionate advocates of pluralist politics. The Coalition has been an experiment in pluralism that is rare in British history. But even worthwhile experiments have their limits and it must be increasingly clear to many Liberal Democrats that they have gone well beyond them.

There are obviously huge risks for the party if they pull out of the Coalition, and some for the country, too. In such circumstances, Mr Cameron might call an early election, win a majority and lead an even more Eurosceptic government. But in the light of recent events, the risks for party and country of sustaining the Coalition are greater.

Liberal Democrats must consider whether remaining partners with the most Eurosceptic Prime Minister in the EU is not more damaging both for them and the country than the option of walking away.