David Cameron arrives at the EU summit as a leader of a divided party and desperately in need of allies. Instead of focusing on doing the right thing for Britain by supporting eurozone reform, he has been spending more time reacting to the demands of Conservatives MPs urging him to throw a spanner in the works.

Many Tories clearly consider that opting-out of the social chapter is more important than the collapse of our main export market. Boris Johnson and several cabinet ministers are in open disagreement with the prime minister's stance. Such divides are now at the heart of the Conservative Party and Cameron has lost control.

It would be easier to sympathise with the prime minister had he not stumbled into a trap of his own making. He was more than happy to play the anti-European card when it suited him, especially when he secured the Tory leadership by pledging to break his party's alliance with moderate European conservative leaders like Angela Merkel.

Now, in order to maintain British influence in a debate of enormous importance to our future, he expects to be taken seriously by the very people he was so quick to shun for the easy applause of his own backbenchers. As a result, he is not invited to the centre right gathering on the eve of the summit at which the most important European leaders are present.

Like John Major before him, Cameron is trapped between the demand for disengagement in the party interest and the need for engagement in the national interest. And like Major, he is too weak to resolve his dilemma with an act of decisive leadership.

The result is a European policy that is two-faced. Cameron's MPs understandably expect him to fulfil his promise of repatriating powers. But then rhetoric collides with the reality of a eurozone crisis that can only be resolved through closer integration among its members.

So Cameron tours Europe urging other countries to press ahead with the kind of political and fiscal union he has always attacked as a threat to democracy and national sovereignty.

Having said that the answer is less Europe for Britain and more Europe for everyone else, he tops it all by demanding that a looser relationship for Britain should be granted without any loss of influence or membership rights. No wonder Nicholas Sarkozy told him to "shut up" at the last summit. Many of our partners can barely conceal their irritation at what they see as a double game.

This matters because there is a risk that with closer political and economic integration among the eurozone 17, key decisions that affect our interests will be taken without Britain and the other non-members. The only way we can maintain our influence is by showing that we are willing to play our part in building a strong and successful EU. It is a matter of building up political capital by working constructively as part of the team.

The last Labour government was very successful at using this kind of positive diplomacy to get the best deal for Britain in European negotiations. We secured the right to opt-in to EU justice and home affairs policies when it is in our interests and remain outside when it isn't. We successfully defended the right of British workers to choose their own working hours under EU law. And despite deciding not to join the euro, we ensured that key economic decisions affecting Britain would continue to be taken with our full involvement.

This was only possible because our partners understood that we were genuinely motivated by concern for the national interest, not by ideological hostility to the idea of Europe itself. Our arguments were listened to with respect because we had earned their trust.

Instead of pandering to his backbenchers and fuelling anti-European sentiment with easy promises of repatriation at some unspecified point in the future, the prime minister should be telling his party some home truths about where our real interests as a country lie.

Cameron's failure to develop a credible and consistent policy on Europe poses enormous risks for Britain. It takes us back to the weak and incoherent leadership of the Major years, but in circumstances that are much more dangerous. The eurozone crisis threatens our economic prosperity and the future of the single market itself.

If Labour were in power, we would have engaged earlier and more constructively. We would seek reassurances that decisions that affect us would not be taken without us. To strengthen these guarantees we would ask for observer status for non euro members at meetings of eurozone members.

We would push for the EU to develop a plan for jobs and growth, which is needed in the UK as well as in the other 26 member states. This government has left our economy more vulnerable to the eurozone crisis.

The question is whether the prime minister is a strong enough position to deliver on these issues. The government is on the sidelines and isolated in the EU because our prime minister is devoting more energy wrestling with a divided party than delivering the best deal for Britain.