Who killed the EU treaty? Was it pre-meditated murder or manslaughter? Some say David Cameron wielded the knife. It is suggested that he went to Brussels with every intention of wrecking the treaty. It was politically impossible for him to deliver his party, regardless of concessions. On this charge, the Prime Minister is either hero or villain, depending on which side you are on.

For others, the crime is one of gross negligence. The list of failings is long and painful; the side-lining of diplomats in the Foreign Office in favour of Treasury officials, a 4am “take it or leave it” position, ambiguity over the impact of British demands on the single market, all topped off with Cameron’s self-inflicted withdrawal from Merkozy’s European People’s Party. Against this sort of backdrop, was success ever really likely?

The killer and their motives will perhaps never be revealed, not beyond reasonable doubt anyway. But for the Liberal Democrats, Nick Clegg has made it plain that regardless of how it came about the veto was bad for Britain. In spite of the blow that these events have dealt, walking out on the coalition – with potentially dire consequences for both country and party – is surely not an option. Clegg is right to push instead for re-engagement with our European partners and to seek to repair any damage done to goodwill and influence.

At the same time, however, it is important that the leadership remains rhetorically robust over this episode. Liberal Democrats should do no more soft-pedalling than is absolutely necessary for the sake of good Cabinet table manners. Voters are divided on Europe – generally more sceptical than positive – but they tend to agree that parties without principles are not worth voting for. The Liberal Democrats have not always found it easy to balance coalition niceties with buoying up the party faithful. Europe is a core issue like no other, so they must tread carefully.

Neither should Liberal Democrats compromise an inch with the Eurosceptic narrative. Contrary to one popular interpretation of events, David Cameron was not mandated to “draw a line in the sand” with the EU, much less to turn diplomacy into some kind of indulgent act of commentary on the wisdom of the Euro. The goal was to secure two strategic objectives in the national interest.

The first was to enable Eurozone states to move towards much closer integration. The second was to ensure that Britain retained sufficient influence and equality within the single market, in particular over financial services regulation. Neither condition was met. The first objective was frustrated and may (or may not) go ahead successfully without British consent. For the second, there is a now even greater uncertainty over British influence on the rules and regulations that govern the single market.

Looking at these strategic objectives it is no wonder that Eurosceptics are so pleased at the outcome. They never supported them. They support neither the success of the Eurozone nor Britain’s place in the single market. While they cheer David Cameron, they are in fact cheering his failure. In failing to meet Government objectives he has, for them, simply furthered the cause of British withdrawal from the European Union.

Liberal Democrats must therefore go back to the original – now failed – objectives and start again. First, Nick Clegg and colleagues must build bridges and remind our European allies why they like Britain being around, i.e., we are forceful advocates for the single market and for competition, one of the two major NATO players in European defence, a country of considerable diplomatic clout (when done competently) and there remains in Britain an outward, global perspective from which Europe benefits.

The party needs to keep Government policy on Europe flexible and agile so as to move with wider European diplomacy and its inevitable shifts in the wake of last week’s decisions. One obvious deal is for the UK to agree to make the EU institutions freely available in return for some kind of observer status and formal consultation on the direction of the new treaty grouping. Nick Clegg should have a central and more public role in achieving this. The party must also encourage business leaders who fear for the loss of British influence to stick their heads above the parapet and explain why they need a voice in Brussels.

There is a huge amount of fatalism about Britain and the EU today, much of it understandable given the circumstances. Our future relations with Europe will be determined in large part by the fate of the Eurozone. Even looking a few months into the future we have no idea whether or in what form the Euro will be with us. We do not know what impact a collapse or contraction of the Eurozone would have on the EU itself. But it is the worst kind of reactionary response to simply throw our hands up in despair and run for an imaginary exit. There is no defence against our proximity to the Euro crisis. But we can do much to prevent isolation.

*Ben Jones was Liberal Democrat Foreign Affairs & Defence Adviser from 2007 to 2010. He is a Director at Interel Consulting.