David Cameron is looking lonely. On the other side of the channel, Germany and France are talking about binding themselves ever more closely in the quest to save the euro. Across the Atlantic, Barack Obama pays lip service to a special relationship with Britain, but that’s about it. The prime minister is in need of chums.

Mr Cameron’s predicament brings to mind the adage that we should be careful what we wish for. His coalition government has been urging Angela Merkel and Nicolas Sarkozy to get on with building a fiscal union. The calculation has been that if the single currency falls apart, Britain’s economic prospects will turn from bleak to cataclysmic.

Yet now eurozone leaders are heading in the desired direction, Mr Cameron finds himself banished. The other day, what had been billed as a full-blown summit with Mr Sarkozy was downgraded by the Elysée to a working lunch. Ms Merkel’s aides say she wants to stay on good terms with Mr Cameron – as long, that is, as he does not get in the way.

British prime ministers have been here before. I recall reporting on European summits at which the only other leader to give Margaret Thatcher the time of day was the then Dutch premier Ruud Lubbers. John Major drove even the kindly Dutch to despair by declaring war on Brussels over, of all things, beef. Gordon Brown’s alternating absenteeism and grandstanding won him few friends among Europeans.

For all that, Mr Cameron is in a tougher position than most. His predecessors could usually lift their spirits with a trip to Washington. Britain’s prime minister was once assured of a warm reception at the White House. That is all over.

To the extent the US still pays attention to the transatlantic relationship, it has only one concern. The administration wants Europe to rescue the euro before the sovereign debt crisis wrecks Mr Obama’s re-election hopes. Without influence in Berlin or Paris, Mr Cameron cannot expect a look-in in Washington.

Mrs Thatcher and then Tony Blair both managed to leverage economic success at home into influence abroad. This is not a trick available to Mr Cameron. British politicians have been indulging in a spot of schadenfreude. Wasn’t Britain clever to stay out of the single currency? The snag is that it ruined things without Europe’s help. Last week George Osborne, the chancellor, foreshadowed a dismal decade of low growth and static living standards. Understandably, others are nowadays disinclined to take lessons in economics from the British.

To the horror of his own diplomats, the prime minister’s first response to the euro crisis was to tell Ms Merkel he did not want to join any of the discussions about the future of the single currency. More recently, he has woken up to the danger of leaving an empty chair.

As soon as eurozone governments share decision-making about fiscal policy they will start making rules that affect all 27 members of the European Union – most obviously in relation to the single market and financial regulation. The City of London looks particularly vulnerable. There have already been clashes about a financial transactions tax and new capital rules for banks.

So what to do if you are Britain’s prime minister? Well, Mr Cameron should start with three “don’ts”. The first says don’t hector. As Charles Grant notes in the Centre for European Reform’s latest bulletin, Germany and France have a Plan B if Mr Cameron climbs on to his soap box: they can bypass him with a deal among the 17 eurozone states.

The second don’t says avoid delusion. Mr Cameron should not think that Britain can lead a powerful new alliance of the “outs”. It tried that 50 years ago with the European Free Trade Area. Sure, the other 9 EU members outside the eurozone have a shared interest with Britain in preventing the euro group from making all the rules. Unlike Britain, though, most of the “outs” want eventually to be “ins”.

The third “don’t” is any attempt to attach conditions to British acquiescence in treaty changes. Tory MPs want Mr Cameron to secure the repatriation of powers from Brussels. Such a deal is for the birds. As Mr Grant observes, asking for more British opt-outs would hasten a Franco-German move to plan B.

As for the “dos”, there is only one. Make friends to influence people. Counter-intuitive as it may seem for the Tories, who have so long demonised Brussels, Britain’s best ally in all this is probably the European Commission. It shares Britain’s interest in preserving decision-making at 27.

Mr Cameron might also take a flight to Rome. Mario Monti, Italy’s new prime minister, is an economic liberal who believes in the single market. There are some others like him both inside and outside the euro group. What’s required is creative diplomacy and some unaccustomed humility. This will not propel Britain to the centre of events. It might leave Mr Cameron a tad less lonely on the sidelines.

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