ANOTHER British triumph in Europe, then.

David Cameron has placed his virility on the table and waved his enormous veto around. So ecstatic are the Tory back benches you would think they actually won the last General Election.

So what has the Prime Minister won, exactly? He seems to think he has protected the ancient liberties of the City of London. This might be one of his bigger delusions. Does he truly believe that if a Eurozone "fiscal compact" gets off the ground its members will be happy to see London continue as the deregulated off-shore home of pirate banking?

Mr Cameron also seems to believe that representing the City's interests is his primary responsibility. This should come as news to the rest of us, many of whom want exactly the reforms of crooked institutions – a transaction tax above all – that are being demanded by Angela Merkel and Nicolas Sarkozy. Mr Cameron's loyalties in this are worth remembering: when push came to shove, bankers mattered most.

So has the Prime Minister preserved Britain's right to a decisive say over the future of the single market? That's the claim. He argues that by refusing to accept a reform of the Lisbon Treaty he has prevented a fundamental change in the nature of the EU. All members, he reckons, remain equal partners.

How so? There are 17 Eurozone countries, plus all the other EU states save Britain, ready to declare that they are, in effect, the single market. The core group will next say that the euro and the market are indivisible. What's good for one is good for the other. They will legislate and act accordingly. Britain's opinion, if anyone bothers to give it a hearing, will be ignored. We will be, as they say, "out of the room".

Mr Cameron has achieved nothing. In fact, he has given Mr Sarkozy and Mrs Merkel exactly what they wanted. France, in particular, needed British myopia and truculence to concentrate the minds of other EU members. Mr Cameron played his part to perfection by trying to block the only reform on offer that might shore up the euro. And Britain, of course, is not even a member of the single currency.

If nothing changes – and it remains a big if – we are on our way out of Europe. It might rest on the difference between de jure and de facto, but no other conclusion is plausible. Britain can be an impotent associate member while the Eurozone-plus create a new union and a new single market, or we can withdraw entirely. Endless opt-outs to placate Mr Cameron's eurosceptics are no longer on offer.

Angela Merkel and Mr Sarkozy have made that much clear. The Prime Minister can no longer influence events within the EU. He says he will not allow a "treaty within a treaty"; most of the rest shrug and carry on. He says he will not allow the British financial sector to be hobbled; the rest say they will make their own arrangements. The City should take no comfort from that.

Mr Cameron's Eurosceptics are content whatever happens. He cannot – and he should have known it – win on their terms. If Britain makes common cause with the rest of the EU they are outraged by the sell-out. If Britain is marginalised, as now, they are "outraged" by the insult and the loss of influence. Either outcome is proof, in their book, that the fundamental relationship between Britain and Europe has been altered.

So they will go on demanding a referendum, and go on pushing for a British withdrawal. There is now no version of the EU, or of Britain's relationship with the EU, that can meet their demands. Why they imagine we can quit the union while retaining a privileged access to the single market is something they have yet to explain.

There is no guarantee that the fiscal compact will work, of course. Persuading 17 countries to submit to budgetary controls, and hence to political control, might be impossible. The peoples of Ireland, Spain, Italy, Greece, Portugal and other nations might rebel, given the chance, at still more austerity imposed – for such will be the language – by Berlin.

Could an Irish referendum be won? Is Ireland even in a position to "harmonise" its corporation tax with the rest of the EU? We will be hearing a lot more about German power in the months ahead. We will be hearing a lot more about democracy, too. The Franco-German plan requires a huge surrender of sovereignty from countries with shaky, patched-together governments. But that's another story.

If Mr Cameron imagines he is acting out a modern version of the old Low wartime cartoon – "Very well, alone" – he is misinformed. His fundamental position was that Britain was keen to see the euro saved, but not if a rescue damaged British interests. Logically, if you believe Nicolas Sarkozy, Angela Merkel and the others, this meant he would rather see the euro collapse than risk reform of the City.

So what if the single currency does fail? How does that help the City of London? Why has George Osborne, the Chancellor, been telling the Lords economic affairs committee that "there would be a significant drop in UK GDP if the euro were to fall apart", and that we would not "bounce back out of it"? According to some reports, the Treasury is pricing the drop at 7% of GDP, equivalent to £100 billion.

Back, then, to our question: what has Mr Cameron achieved? He has not "safeguarded the City", helped to stabilise the euro, guaranteed a British role in the future of the EU, or ensured access to the single market. He has acquired no allies: the disdain for Britain's position has been palpable. Even the trio who at first seemed to support Mr Cameron – Sweden, Hungary and the Czech Republic – look likely to go along with the treaty reform process.

Above all, the Prime Minister has failed to win hearts or minds, at home or abroad. Sceptics remain sceptics; the core European countries are set on their course. In City boardrooms, meanwhile, one fact is understood perfectly well. EU decisions on financial regulations are made according to the qualified majority voting system. In other words, Mr Cameron has no real veto in the argument he claims matters most.

He will get his dose of applause from his back benches and the Tory press. Boris Johnson was first to the microphones yesterday to praise his leader and rival. That sort of chatter will subside when reality sinks in. The simple fact is that Mr Cameron has risked everything in terms of Britain's influence and EU membership for the sake of the bankers, those guardians of our economic welfare.

Thanks to the obsessions of his back benchers, obsessions that have bedevilled Tory leaders for a generation, Mr Cameron probably believes he had no other choice but to exercise his veto. He acted, in fact, as though the interests of the party that failed to win a mandate in a general election were synonymous with the national interest.

In one sense, it hardly matters. We are heading for the exits. A little flag might fly in Brussels or in Strasbourg for years to come, but Mr Cameron has brought matters to a head. Henceforth, Britain will be a spectator in Europe. Irrelevant is such an ugly word.