The reverberations from David Cameron's decision last Friday to wield Britain's EU veto continue to multiply. We know the real reasons for the British veto are domestic. Cameron believed any agreement would split his coalition government, initiate a UK referendum, and lead to the full departure of the UK from the EU. So Cameron opted in by staying out. Despite much international negativity and domestic anxiety, this has created a new and wholly unrecognised strategic opportunity for both the UK and the EU. Apart from selling more goods to the Bric nations, Britain lacks any discernible foreign policy and in particular it has no vision and nothing to say on Europe. This is fundamentally dangerous for Britain and the world – it undermines the UK's role in international affairs, and imperils real and recent European achievements: the liberation of Libya and the bilateral defence relationship with France to name but two.

So what is this opportunity? Currently Britain remains the sole defender of a European Union that has been all but captured by the demands of the eurozone. Once it had decided on the veto, the UK was legally and morally correct to resist plans by the eurozone countries to use the institutions of the 27 member EU to secure the 17 members who use the euro. The UK is now rightly defending the European commission and the European court of justice from being subverted by eurozone demands to use these institutions to police any putative euro settlement.

Merkel and Sarkozy were trying to tie the institutions of the EU to the interests of the eurozone in order to give Germany some further legislative hold, via the courts and the commission, over the countries whose debts it is planning to underwrite. By any objective rationale this needs to be resisted, not for the sake of the UK but for the sake of Europe.

It is perfectly rational to argue that the euro is not in the interests of Europe and that it is vital to maintain an EU apart from the euro because the project to stabilise the currency and its multiple sovereign debt problems may well fail. There needs to be a pan-European structure which countries can still adhere to if the common currency collapses.

Out of perceived domestic necessity Cameron has created a new European invention that will have an increasing attraction for the other European nations that fear political exclusion or economic destruction by the French/German axis. Indeed, the prime minster has already spoken of approaches from other nations outside the eurozone such as Sweden and the Czech Republic, anxious about what they have signed up to, as well as countries such as Ireland equally concerned about the consequences of the new arrangements. As such Cameron can and should position himself as the defender of a European escape route from a project that has every chance of collapsing in dangerous acrimony.

Maintaining the EU and eurozone as separate is a double insurance against the future. Firstly because the proposed remedy at Brussels to the euro crisis is little more than the old and failed growth and stability pact but without the growth – as yet it is hardly likely to work as it fails to address the current crisis and sets up a dysfunctional system for dealing with a settlement yet to be achieved. Any genuine euro solution is equally difficult to imagine as it relies on the ECB finally accepting its role as the lender of last resort while forgoing any euro-wide mutualisation of debt. No wonder the Germans are anxious for a judicial and policing role, without this they simply have no security for what they are planning to do. The current proposal agreed in Brussels is a misconceived attempt to regulate a settlement that does not exist, moreover the timing is out of kilter with the bond markets and this "fiscal agreement" may well be priced out of existence before any resolution by the eurozone is achieved in March of next year.

Moreover, even if the new intergovernmental treaty works it also risks medium-term failure. It will mean damaging austerity for years, administrated by a judicial centre that will permit no variation or innovation, and will drive a wedge between Europe's citizens and undemocratic technocratic rule. The social disorder that we have seen in Greece will likely pass to Italy, Spain and Portugal – reviving both European nationalism and hatred of German hegemony – exactly what the EU was designed to avoid.

Britain needs to stress that it sees the euro as the great danger to Europe and, rather than bizarrely pushing for its centralisation under a German economic aegis – a provision that will ensure permanent proletarianisation for the southern nations – it needs to seek and create a new EU growth pact for those who wish for an alternative outside the euro but in Europe. For the common currency area that might mean separate euro zones or parallel currencies with greater or smaller spreads in relation to the euro. Rather than letting domestic policy-needs trump any international dimension, if Cameron is clever he could utilise one to augment the other and create a euro opt-out for nations for whom saving the euro would mean their own democratic erasure and impoverishment . If Cameron can make the most of this policy opportunity he will have created a vital exit strategy for European nations from a policy and a position that has every chance of failing. And, in time, Europe may thank Britain once again for saving them from themselves.

• This article was amended on 16 December 2011. The original referred to the proposal agreed in Lisbon. This has been corrected to Brussels.