If it all ends on Monday, with the Greeks voting for austerity in order to keep the euro, the first far-left party to hold office in modern Europe will be judged by its critics a failure.

By calling a referendum, Syriza has gambled that it can strengthen its hand in negotiations with its lenders. But with no extension to its bailout programme, and emergency funds from the European Central Bank (ECB) on a knife-edge, the move has prompted this week’s “bank holiday” and the rationing of cash at ATMs.

With the opposition and business groups warning of economic catastrophe, Syriza – which means “coalition of the radical left” – faces a nailbiting week. What is at stake is whether this party of around 20,000 members can hold the left half of Greek society together long enough to force the lenders to negotiate – or whether it will crash and burn under the pressure of popular anger and disillusion.

If they win, on the other hand, they will be seen as heroes by opponents of austerity across Europe.

But win or lose, Syriza in office has been a work in progress, impossible to read for people ignorant of Greece, let alone people who don’t know there are subcategories to moderate Marxism.

People wait outside a closed National Bank of Greece branch in Athens. Photograph: Yannis Kolesidis/EPA

Greece under austerity has become frenetic. Athens right now is slick with perspiration; every public space is charged with hormonal tension and political disagreement – even the bakery where you buy your morning bread. The politics are brutal. Last week, stick-wielding anarchist youths attacked the HQ of the Antarsya – a far-left anti-capitalist party – because the latter had tried to make them pay to go into a music festival when the anarchists thought it should be free.

I’ve seen, in the bohemian Exarchia district, a troupe of black-clad 15-year-olds distrupt a whole street full of similarly bohemian cafe-goers on a Saturday night, using petrol bombs and flaming rubbish bins, simply because “creating mayhem” is their doctrine.

Athens has become, in short, the stage for flamboyant acts of self-dramatisation: sporadic riots, public kissing, street theatre and ill-advised scooter techniques. It is, to use a phrase Huxley once used about Shanghai, “life with the lid off”, and for the same reasons: “so much life, so carefully canalised, so rapidly and strongly flowing”.

Antonis Vradis, a geographer at Durham University who has studied the impact of repeated waves of unrest here since 2008, describes how the youth networks have been preparing for this week’s “rupture” with the ECB: “They are creating structures you can’t default on. Self-organised clinics, the social centres you see all around you. Structures that will help them survive.”

I meet Vradis in Floral cafe on the corner of Exarchia Square. He points out that the building – shabby as it is now – is a Bauhaus masterpiece. More importantly, during the 1944 uprising against the British, “the communists were snipers on the roof”.

The young here live always with a portion of their brain operating in the past. They don’t need wall plaques. When they move through Exarchia, or Syntagma, or up the side of parliament towards the mansion prime minister Alexis Tsipras now occupies, they can “see” where the resistance fighters died; where the students of 1974 stopped a tank.

Alexis Tsipras in parliament. Photograph: NurPhoto/Rex Shutterstock

It was the young people radicalised amid this landscape who pitched a tent camp outside parliament in 2011. They organised a movement most foreign journalists didn’t see: local assemblies in small squares across the city and its suburbs, where young mums, migrants and outraged pensioners could have their say. The communists denounced them; the socialists sent riot police to disperse them; Tsipras is said to have looked out of the window of his office and delared: those are the people who will put us into power.

But Syriza is different. Syriza is a coalition whose colours are red for socialism, green for ecology and purple for feminism. But it is primarily red. It was born out of Eurocommunism – when the communist parties of the west declared loyalty to parliamentary democracy instead of Moscow. Its most influential activists are aged 50 and above: people who have read all three volumes of Karl Marx’s Capital, plus the Grundrisse, Theories of Surplus Value and Friedrich Engels’ Anti-Dühring. A lot of them are MPs now, or special advisers: you’ll find them in greying huddles in their old haunts – the radical bars and cafes of Exarchia and Plaka.

How this generation of Greek leftwingers broke out of isolation is of more than academic interest. They have managed – for the first time in modern history – to form a government that defied the global finance system, and to do so with flair.

Their strength was that they understood the significance of the youth revolts of 2008 and 2011. Some pitched their own tents in Syntagma Square and were tear-gassed out of it. But in the process, the party built something more official and resilient.

Syriza supporters in 2014. Photograph: Petros Giannakouris/AP

Their weakness, it turns out, starts with Nicos Poulantzas. Poulantzas was a Greek intellectual of the new left who famously clashed with Ed Miliband’s father, Ralph, in 1969 over the nature of the capitalist state. Miliband said the state was “capitalist” because personally controlled by the business elite. Poulantzas said the state was structurally capitalist – independent of the will of individuals.

Poulantzas evolved a dual strategy for the Greek left in the 1970s: first, to encircle the state with social movements, which were not to be controlled by any party but allowed to become expressions of popular democracy. And at the same time, to enter the state, democratise it and use it to pursue social justice. Poulantzas killed himself in 1979, but his ideas guided the precursor organisation to Syriza. Not many people remember now, but the party’s predecessor, Synaspismos, joined a short-lived coalition government with the conservatives in 1988, and a national government thereafter.

Nikos Poulantzas. Photograph: Sophie Bassouls/Sygma/Corbis

In the runup to its election victory, Syriza got a chance to execute the Poulantzas strategy of the march through the state: it won the Euro elections and the vital prefecture of Attica, where its candidate was protest veteran Rena Dourou. Then it won state power – but that has turned out differently.

When Tsipras took over the Maximos Mansion, the PM’s residence, the outgoing government removed all computers and all soap. There is soap now, and computers, though no Wi-Fi for security reasons. Tsipras rules from one side of a marble hall; the other side is the cabinet room. In the basement are secure meeting rooms and offices. At the weekend, you will often find somebody’s children crayoning on the floor. The ceremonial guards, in their white tunics, sip freddo-cappuccino on a narrow terrace, alongside press photographers and armed bodyguards.

In power, Syriza has discovered the unguessed secret of the Greek state. Without oligarchs, it is inefficient. So thoroughly did the old parties use patronage to run the operation that they barely needed a civil service, or the shock absorbers provided by independent regulators and quangos normal in a state such as Britain. I have seen ministers confronted with ridiculously detailed operational decisions, such as the appointment of a new boss for the state TV channel, which in Britain would be delegated to a regulator, but in Greece fell to minister of state Nikos Pappas. Finance minister Yanis Varoufakis routinely handles his own press: though he has press officers drawn from Syriza, the actual press operation of the Greek state is barely engaged.

Yannis Dragasakis, Greece’s deputy prime minister, was in many ways the embodiment of Syriza’s long-term dreams. His team of advisers included those most attuned to the “horizontalist” agenda emerging out of the networked social movements; people whose main desire was to nurture the 70-plus small-scale economic experiments they had promoted: local currencies, Wi-Fi networks in the mountains, producer co-ops.

But Dragasakis was given “operations”: to operate the government, to firefight the banking system, to sort out the state energy company. Those who expected his department to unleash a wave of entrepreneurship and experimental projects have had to wait.

Greek finance minister Yanis Varoufakis. Photograph: Daniel Ochoa de Olza/AP

Probably the most challenging job in Greek journalism right now is to work for Avgi, Syriza’s newspaper. It is a daily, with professional graphic design, but suffers because nobody can decide whether it is meant to carry the party line or to be a voice for the mass base, and therefore a pain in Tsipras’s butt. When I meet editor-in-chief Giorgos Kiritsis, he is surrounded, almost symbolically, by fading newsprint and old posters. He chain-smokes and pulls up a Facebook page on which someone has posted a 50,000 drachma note with Kiritsis’s face on.

Nobody knows what 50,000 drachmas will be worth if Greece defaults on its debts, but Kiritsis and his colleagues have for months been exposed to the basic dilemma of Syriza. It is a coalition – including the hard, pro-Moscow left who want that drachma note to become real; a centre around Tsipras who wanted to try to shrug off austerity within the euro; and former social democrats who want, at all costs, to do a deal with the lenders.

It was not until 4 June that Tsipras became convinced that his original strategy – to go on paying the lenders while negotiating the fine detail of an accord that never seemed to come – was fruitless. It was at this point that the forces in Syriza realigned leftwards and the strategy of the troika (the ECB, IMF and European Commission) – which had always been to split Syriza, forcing Tsipras and his own moderates into a coalition government with the centre parties – was in tatters.

The ultimate question for Syriza, with the banks closed and the referendum due, is: can it now function as a movement? It has ridden to power on the back of social movements but, unlike Podemos in Spain or Sinn Féin in Ireland, has never really been a mass movement itself.

Graffiti in Athens. Photograph: Petros Giannakouris/AP

In the middle-class suburb of Chalandri in northern Athens, the mayor, Simos Roussos, has to organise the referendum and simultaneously keep the machinery of government going. Roussos was elected on a joint slate between Syriza and Antarsya party. He tells me the council’s gas supplier refused a delivery on Monday – not on the grounds that he wouldn’t get paid, but on the grounds that he didn’t like what Syriza is doing.

We meet at a council-run clinic where, after midday, the official GPs and psychiatrists give way to a team of volunteers. It is run this way because the austerity under the previous govenrment means they can’t staff the clinic with paid employees. The volunteers include doctors, psychologists and qualified pharmacists, but I find them engaged in the menial task of hand-sorting donated medicines. They note the sell-by dates, count the pills and sort them. This is Syriza’s mass base – but it is not Syriza.

Syriza was always a party before it was a movement. The early polls taken since the referendum was called indicate it still has mass support. The unanswered question is whether it can hold the leftwing half of Greek society together amid this week of chaos.

Nineta, one of the volunteers at the clinic, tells me people are frightened, but that she is totally behind what Syriza has done. The antidote to fear is solidarity, she says. But nobody is sure how much solidarity can survive if the banks stay closed.