Leading article: A split Coalition weakens Britain's voice in the EU

Mr Clegg needs to show, despite the evidence, that his party will not be steamrollered

For the last Prime Minister's Questions of the year, Nick Clegg was back on the Government frontbench, in his customary place beside David Cameron. It was a calculated show of unity after Monday, when both the Deputy Prime Minister and his Liberal Democrat colleagues staged an equally calculated absence. The Prime Minister suffered some ribbing from Ed Miliband, having to listen as his own words about the joys of Coalition and its "more collegiate approach" were flung back at him, but he had no barb sharp enough to pierce Mr Cameron's retort: "It's not that bad; it's not like we're brothers or anything."

So the message to the country at large was that all is fine; the Coalition is back on an even keel, and – as Mr Cameron almost put it – "So the Conservatives and Liberal Democrats don't always agree on Europe. What's new?"

The difficulty is that there is something new since this time last week, or rather several things. The first is that Mr Cameron is now riding high in the polls, at least higher than before. This increases his authority in relation to his Coalition partners. The second is that Eurosceptics across the land have the wind in their sails. If pressure for a referendum on EU membership now builds, Mr Cameron might find it hard to resist.

The third is that the pro-European Mr Clegg, and his likeminded Liberal Democrats, were shown to have zero clout when and where it mattered, between 1am and 4am in Brussels last Friday. Until that point, the Coalition partners had made common cause, professing the belief that saving the euro was in Britain's best interests. From the way Mr Cameron wielded his veto, from the way he stood quite alone against the 26 other EU countries and from the way he then returned as a conquering hero to Chequers that night, it was almost as though the Coalition had never been.

And there is a fourth change – doubtless the least significant in the Eurosceptic canon, but the most damaging for Britain's longer-term interests. After last Friday, this country has been more isolated in the EU than it has been at least since the beef war of the 1990s. Sections of British business fear the effect that Britain's exclusion from any future EU financial arrangements might have on the City of London, whose interests Mr Cameron claimed to be defending. There are doubts, too, whether Washington will still prize the "special relationship" if Britain ceases to be its privileged entry point to Europe. For all these reasons, Britain should already be extending feelers to key EU members, such as Germany, and potential allies, such as Sweden and the Czech Republic, who initially voiced misgivings. What we see, though, is the Liberal Democrat leader alone calling for moves to "ensure that our calm, reasoned and engaged voice is heard positively within the EU institutions". And what we hear are reports that he is working quietly to mend fences Mr Cameron has broken.

Mr Clegg's rationale is obvious. He needs to show his party and the country that he is keeping the Europhile faith – a distinctive Liberal Democrat policy. He also needs to show, despite the evidence, that he will not allow his party to be steamrollered by the Coalition senior partner. The EU summit, however, made that look like so much wishful thinking. And unless the Prime Minister associates himself with Mr Clegg's efforts – something that jeopardises his shiny new Eurosceptic credentials – how seriously will the rest of Europe take them?

It is just possible that Britain's best chance to re-engage will come in the unravelling of last week's agreements, which looks more likely as each day goes by. Even then, though, returning to the table on an equal footing will be far harder than it might have been had Mr Cameron not generated so much ill will with a veto that could turn out to be unnecessary, as well as unwise.