Since it was founded 100 years ago as an antidote to French government propaganda during the first world war, Le Canard enchaîné has remained a thorn in the side of France’s great but not-so-good.

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For a century, the satirical newspaper has provoked the wrath of presidents, politicians, tycoons and other public figures, to the point that in the 1970s even mentioning its name in cabinet meetings was reportedly a sackable offence.

Another Canard legend recounts how local politicians, who found their peccadillos and dubious dealings exposed in the weekly, would rush to their town’s press kiosk and buy up every copy in an attempt to salvage their reputations. Such is the paper’s influence that even today government ministers and rival newspapers pick up copies of Le Canard hot off the press on Tuesdays to see what scoops it has published before it hits the news stands.

With a new book out celebrating its 100 years of investigative reporting, cartoons and general mischief-making, Le Canard’s editor, Érik Emptaz, admits the year has been one long centenary party. “The first ever Canard enchaîné was published in one of the most bloodiest years of the first world war. It ran for five weeks, then stopped and started again the following year. It means we’ve been celebrating for the whole year,” Emptaz told the Observer.

Like its younger, more cartoon-based sibling, Charlie Hebdo, Le Canard enchaîné is a French media symbol: a weekly newspaper with no advertising, no promotion, and no owners except the writers and cartoonists who produce it. It has a website – almost grudgingly – on which little is published, and relies on paper sales. At a relatively modest €1.20 (£1) per copy, it still makes money in an increasingly depressed media market.

The eight-page weekly, published on Wednesdays in black and white with the occasional headline in tomato-red print, currently sells around 400,000 copies a week and made a €2.4m (£2m) profit last year, which went into a “reserve” fund – now €123m – a substantial insurance policy against lean times.

“Nobody can put pressure on us because the only pressure that can be put is economic – a threat to remove advertising or publicity or from shareholders, and we don’t have either. That makes us independent and immune to pressure,” Emptaz said. “We cannot be influenced and that’s our strength. Nobody and nothing is off-limits, except people’s private lives. We don’t go there.”

Emptaz believes Le Canard’s role is to hold everyone to account. It leans to the left, but is “neither right nor left but in opposition”, he said. Its weapons are irony, humour and a contrarian defence of an opposing view with the explicit intention of revealing its cracks and weaknesses.

The Canard is proud of its network of contacts and informants, said Emptaz – some of them in very high places. He said its investigative journalists “check the facts, check again and triple check and then add the humour”.

In 1993, after Le Canard revealed that Pierre Bérégovoy, prime minister under Socialist president François Mitterrand, had accepted an interest-free loan from a businessman, Bérégovoy committed suicide. The Canard sold out that week, but declined requests to reprint because it refused to profit from the tragedy.

The weekly’s journalists are famously barred from accepting any kind of official award, such as the Légion d’honneur, in line with the paper’s independence.

The first Canard enchaîné appeared on 10 September 1915 promising to publish only “rigorously verified inexact news”. The paper’s founder, Maurice Maréchal, a former weather reporter, explained his motives for publishing a satirical paper. “When I hear something scandalous, my first response is outrage, my second is to laugh. It’s harder to laugh, but more efficient.”

The French word canard (duck) is slang for newspaper, and the name is a reference to Socialist Georges Clemenceau’s newspaper L’Homme libre (The Free Man), which was forced to close by government censors and changed its name to L’Homme enchaîné (The Chained-up Man).

Refusing to submit to censorship during the second world war, the paper closed, reopening in 1944. Resistance hero Pierre Brossolette, who later committed suicide after being tortured by the Nazis, told a friend: “The French will know when the war is over, when they can read the Canard enchaîné again.”

Emptaz says the paper regularly receives threats of violence, and since the attack on Charlie Hebdo in January 2015 – when terrorists gunned down 12, including cartoonist Cabu, who also worked for Le Canard – its offices have been under police protection.

But the greatest threat, says Emptaz, is more prosaic: sales are being hit by the closure of Paris’s newspaper kiosks, making it harder to buy any publication in its physical form.

So will Le Canard enchaîné become a digital duck? Emptaz looks pained. “If we do, we won’t be giving it away online for free. Without advertising, that would be suicidal,” he said. Le Canard enchaîné – 100 Ans is published by Seuil