Among the chic bars along Thessaloniki's historic waterfront, one restaurant stands out. "We want our money!" reads a banner dangling from the terrace of an American-themed diner and grill. Inside, 12 staff have changed the locks, are serving cans of supermarket beer to supporters and taking it in turns to sleep nights on the restaurant floor in protest at months of unpaid wages and the restaurant's sudden closure. This is the new symbol of Greece's spiralling debt crisis: a waiters' squat.

Margarita Koutalaki, 37, a softly spoken waitress, divorced with an 11-year-old daughter, worked here part-time for eight years, earning about €6.50 (£5.70) an hour. Now she is taking turns to sleep on an inflatable mattress in an upstairs room, guarding the squat, while her parents babysit her child.

"I'm owed about €3,000 in unpaid wages," she says, warning her plight is shared by legions of workers all over Greece who are waiting for months for outstanding pay from struggling business owners. "At first we were told we'd be paid the following month, then the pay stopped completely and we were told by phone that the restaurant was closing. We're still working, we're keeping the place going, providing food and drinks to our supporters. We've got more clients than before. This protest is all we can do. It comes naturally."

The waiters serve cheap drinks and cut-price dinners to a new clientele of leftists and protesters from the four-month-old "indignants" movement, who would previously never have set foot in this bastion of imperialism, the Greek franchise of US giant Applebee's. A banner in English tempts tourists with cheap souvlaki and meatballs "in support of the workers".

It is one month since Greece was paralysed by a general strike over harsh austerity measures, with mass street demonstrations and running battles between police and protesters in Syntagma Square, Athens.

Greeks are more distrustful than ever of their political class and its ability to lead them out of the crippling financial crisis. Polls show growing contempt for all parties and the discredited political system. Unemployment is at a record high of 16% – far higher for young people. Those lucky enough to still have a job have suffered dramatic salary cuts and tax increases.

Doctors and nurses recently staged walkouts over hospital cuts. Taxi drivers have hobbled Greece with strikes in the past two weeks, protesting at government plans to open up the industry. Their tactics included blocking ports and opening the Acropolis ticket office to let tourists in free.

Crucially, Greece's long-running "civil disobedience" movement, where ordinary citizens refuse to pay for anything from road tolls and bus tickets to extra doctors' charges, has not fizzled out in the summer holidays. The "We Won't Pay" offensive is championed as the purest form of "people's power". Organisers warn it could gain renewed force in September as the government launches a new round of financial restraint.

On the main Athens-Thessaloniki road, as drivers file back into Thessaloniki from a Sunday at the beach, a crowd of civilians in fluorescent orange safety bibs stand guard at the barriers to the main road toll into Greece's second city. Their jackets are emblazoned with "Total Disobedience". They push aside the red-and-white barriers and wave drivers through without paying the €2.80 toll. Banners read: "We won't pay", and "We won't give money to foreign bankers". Drivers gratefully drive through, some giving the thumbs up.

"We'll see a resurgence of civil disobedience in the autumn," says Nikos Noulas, a civil engineer from Thessaloniki, in a city centre cafe as he rolls out a series of posters championing the refusal to pay.

Living a 40-minute drive from the city centre, he commutes by motorbike for what scarce work remains, but avoids paying for bus tickets or tolls. He also stages supermarket ambushes, handing shoppers big protest stickers to place on any goods they consider ludicrously expensive. Milk is a favourite. Noulas and his group fill trolleys with goods and ask the manager for a 30% discount. When refused, they abandon the full trolleys at the till.

He acknowledges that a recent police clampdown has made things harder: "If a police officer is watching, there's little choice but to pay a road toll." But he says breaking the law by not paying small tolls or bus fares is far less serious than corrupt politicians and cartels which, he claims, ran Greece for decades with impunity. "This has taught us that the Greek people can resist. It has ignited public sentiment," he says.

The road-toll protest movement began more than two years ago outside Athens to counter what is seen as an extortionate and corrupt road toll system, with drivers expected to pay for stretches of road that have yet to be built. Some residents face paying more than €1,500 a year in tolls to get around their own neighbourhoods.

By the start of this year, the movement was flourishing and included refusals to pay for Athens metro tickets, with protesters covering ticket machines with plastic bags, as well as a long-running bus fare boycott in Thessaloniki after price rises by state-subsidised private firms. Others refuse to pay their TV licences.

Leftwing parties became involved, boosting the campaign's visibility. By March, more than half of the Greek population supported the "We Won't Pay" notion. The government heaped criticism on what it deemed an irresponsible "freeloader" mentality, warning that the non-payers would bring the country into disrepute and were starving the state of vital revenue from transport services. New laws were brought in on ticket evasion and police cracked down.

George Bakagiannis, an IT manager from the Athens area, has avoided paying road tolls for two years, simply stepping out of his car and pushing open the barrier at toll booths. His group stages toll-booth ambushes for two to three hours several times a week, waving drivers through without charge.

He has branched out into demonstrations against the €5 fee for doctors' consultations. He says: "We go to the hospital and close the cashier's room, telling people, 'Don't pay, we're here.' This isn't our crisis, it's the government's crisis. They steal our money; they're stealing our lives. Now they want us to believe even our savings aren't safe in the bank. This movement will grow in this autumn because things are so bad now that people genuinely don't have the money to pay."

The social commentator and writer, Nikos Dimou, says: "It's the beginning of a divorce between the Greeks and their politicians. That's what all these movements have in common: they are all about a loathing and abhorring of the political class."

In Thessaloniki, Greece's second city, feelings run high. The "indignants" had their tents forcibly cleared from Athens' Syntagma Square this weekend, but Thessaloniki's ancient waterfront fortification, the White Tower, is still surrounded by protest tents and draped in banners reading "For sale" and "Not for sale."

Northern Greece has been badly hit by the crisis. Businesses began closing long before the full force of the financial meltdown. So many people are too poor to regularly use their cars and so many businesses have ground to a halt that Thessaloniki's municipality has claimed a vast improvement in the air quality of the notoriously congested city. On 10 September, when the Greek prime minister George Papandreou appears at Thessaloniki's famous international fair to unveil his new economic measures, he will be met by demonstrations.

Thessaloniki protesters are using flash-mobbing, where crowds turn up unexpectedly to picket banks and public buildings. The latest target was the German consulate, where dozens of demonstrators chanted and spray-painted the pavement, demanding the European Union did more for Greece as plainclothes police looked on.

At the demo on 20 July, Barbara, 30, a Greek language teacher, who did not want to give her surname, said she was serving coffee in a bar for €30 per nine-hour shift on the black economy. She lives with her father, a pensioner, and mother, a shop owner who is deeply in debt.

"No one is hiring, I can't find teaching work or private lessons. There's no hope for a decent life. Half the people I know are unemployed; the other half are on the edge of it. Anyone who can afford to go abroad is leaving," she says.

At the White Tower, Antonis Gazakis, a language and history teacher, says he is struck by how novices are now joining the protests, from myriad political standpoints, left to right, many with no links to parties or any history of protest. All were throwing themselves into debating how to change what they see as a corrupt political and parliamentary system. "Political history is being made in Greece," he says. "That's why I'm staying around this summer. The last time people went out into a square demanding constitutional change like this was 1909. This is a golden opportunity, a paradigm shift. Greece has woken up."