The Greek referendum call is, while it lasts, effectively a plebiscite on euro membership.

Image copyright Getty Images Image caption Papandreou announced on Monday that he would put a hard-fought rescue deal to a referendum

I say "while it lasts" because the opposition is mobilising a parliamentary manoeuvre to bring down the government, which may succeed - returning Europe to its status quo of containable trauma.

If Greeks reject the 50% controlled default on the debts they owe to the banking sector, then the arithmetic I revealed on Newsnight on the eve of the Euro summit comes into play - without a 50% haircut, and a further 130bn euro bailout, on top of 110bn, Greek debt spirals out of control and the country goes bust.

At this point, the value of the debt falls to maybe 10% of its face value and Greece has broken all the rules of euro membership.

The euro leaders will be faced with the option of a forced transfer of taxpayers' money to shore up the entire Greek economy with no surety, and no "local representatives" as currently planned. Or Greece leaves the euro.

Most political economists I speak to believe this has been the logic all along, and brave though it has been for Prime Minister George Papandreou to try and buy time to do a proper structural reform of Greece, the implosion of Spain and Italy has robbed him of that time.

Greeks - even those fiercely opposed to Pasok from the left and right - are resigned to the fact that the country faces years of painful restructuring. The real question at issue is a) under whose control and b) in whose interest?

It is for this reason that, while the Greek CP wants out of the euro, the growingly influential far left parliamentary group SYRIZA does not, and neither does the hard-right religious party LAOS. Everybody can see that an external devaluation will be chaotic, painful and cause its own kind of social unrest, just as the attempted internal devaluation is doing.

But events are moving fast. Even as the Greek centre-left toys with the concept of repudiating "odious" debt, as per Latin America in the 1990s, the debt is being concentrated into the hands of other sovereigns - the European Central Bank (ECB), the International Monetary Fund (IMF), other governments…

The reason the markets are scared is not just because of the difference between 50% and 90% default, it is because in the old scenario (AKA the one we agreed on last Thursday morning!) this sovereign-held debt was out of the reckoning. An "Oxi" vote (it means "No" and was scrawled on thousands of banners hung from balconies last Thursday) would signal default across the whole range of debt, causing new turmoil for European states.

What caused Mr Papandreou's sudden move? Even some of the MPs closest to him had no idea it was going to happen.

Many of my Twitter correspondents suggest it was the vehemence of "Oxi Day" last week, leading to clashes between parading soldiers and protesters and local Pasok politicians getting hounded off the parades.

Pasok remains a very well rooted social democratic party, with multi-generational networks inside every village. If the village guys start ringing up and saying - there is no way we can hold it - Mr Papandreou is politician enough to hear this.

Another potential reason is capital flight. Anecdotal evidence suggests that the Greek elite are buying up property in London just as fast as they can find berths in Poole for their yachts. They are voting with their spinnakers, on the basis that the game is up. In any future Greece on offer, they will have to start paying taxes and they do not want to.

One banker told me the Greek super-rich have mostly left.

The one thing governments have that investment banks do not is intelligence services with the power to wiretap people. If you ever wonder why serving politicians go grey so quickly, it is in part because they see the intelligence. So Mr Papandreou may have looked at the file and said, I can't sell this to my party, nor to my voters, and the business elite are emigrating en masse, so throw the dice.

Referendums are, always, basically a coin-toss, an all-chips on the black romantic gesture. Right now, the scale of EU-level mobilisiation to dissuade Mr Papandreou is huge.

But if Greece votes no - and goes for euro-exit - there are several plans in the process of being published that explain what you have to do. Close the banks for days, ration food and energy, institute strict capital controls - with most probably a few fast patrol boats at Glyfada harbour to check every departing yacht for cash and bonds.

Later, you get massive devaluation, with inflation; your non-sovereign debts become instantly doubled so you cannot pay them (i.e., the stock of Greek private debt to external lenders, for example, or, intra-corporate debts).

Finally, you get the chance to become competitive again. (I base this on SOAS professor Costas Lapavitsas' upcoming document, which he has verbally outlined to me).

However, despite this very, very unappealing prospect, you are at least in control of your own economy and you do not have foreign civil servants dictating what ministers can do.

One reason so many Greeks have told me this route is impossible is because there is no Kirchner - no left-leaning autarchic politician who can pose as the tribune of the nation and create a narrative around the default process, as Nestor Kirchner did in Argentina. Nobody on the right wants to do it either. And that is Mr Papandreou's gamble - that nobody outside the KKE will present a coherent alternative to a yes vote, and that the KKE does not want power.

That is how it looks from the balcony of a small hotel in Cannes this morning. When the politicians get here, I will let you know what the whites of their eyes are telling me.