PRESIDENT Nicolas Sarkozy received a bullet in the post last week with a letter threatening to kill him. Meanwhile, several executives, including three Britons, were locked in their offices by workers in protest against redundancies.

France is in a rebellious mood and an outbreak of “bossnapping” is just one symptom. The traditional preference for direct action over debate produced rioting in Strasbourg and Corsica, in which buildings were set ablaze by the mob.

Angry manifestos and anti-establishment screeds are proliferating in bookshops, one of them advocating the sabotage of IT and electricity networks. It has sold 15,000 copies.

Police were last week trying to determine if cuts in the gas supply to parts of Paris, Toulouse and Montpellier were the work of union militants hoping to put pressure on bosses over pay. There have already been attempts to sabotage trains.

No wonder “Sarko” is worried. It is the second time this year he has received a bullet in the post from an unknown enemy. His prime minister and the interior minister have also received them. The only clue for investigators is that all the envelopes were posted in southern France.

Just as unnerving for him is the prospect of social chaos. With the approach of May Day, when hundreds of thousands of protesters are expected to pour on to the streets, the president has been warning advisers that France could be on the verge of one of its periodic upheavals, such as the student uprising in 1968.

A penchant for street protest is as much a part of the national character as a lingering affection for the outdated Marxist creed. But the spate of bossnapping over the past few weeks has dramatically fuelled the impression of a country in revolutionary ferment.

Ian Bushell, the finance director for Scapa, a British adhesive factory, spoke of “disappointment” at seeing the tactic used by militant workers against three British executives held in the firm’s French plant for 18 hours on Wednesday.

“We’re aware that in France there’s been a number of circumstances in which unions have held hostages, but it wasn’t envisaged in our case,” he said from the company’s headquarters near Manchester.

In Paris, François-Henri Pinault, the head of Gucci, the fashion company, was held captive for an hour by workers protesting at job cuts. Several other bosses, including the French director of Sony, and Nicolas Polutnik, head of the Caterpillar bulldozer plant in Grenoble, have been shut in their offices.

Sometimes the kidnapping has seemed like punishment: workers at the US-owned Fulmen battery factory in Burgundy forced Alain Royer, their boss, to accompany them on a march wearing a T-shirt emblazoned with the number of people he had dismissed at his firm. “It was humiliating,” he said.

Even so, a poll found nearly one in two French voters supported bossnapping as a way for workers to express their grievances. In an effort to exploit the mood, politicians of the centre and left have bent over backwards to express sympathy for the bossnappers.

Bosses have traditionally been painted as blood-sucking ogres – a legacy, perhaps, of the revolution in 1789 – but their villainy is seen as greater than ever after stories in the press about fat cats awarding themselves vast bonuses.

Ségolène Royal, the former Socialist presidential candidate, acknowledged that it was illegal to deprive someone of their freedom, but said there were times when “workers must smash the barriers of absolute injustice”.

Martine Aubry, the Socialist leader, adopted the rhetoric of the far left to decry not the practice of bossnapping but the “social violence” being perpetrated against workers.

Not only does Olivier Besancenot, a Trotskyist postman who leads the new AntiCapitalist party, support the bossnappers but he is one of them. He and a band of 50 striking followers recently held a post office chief hostage for several hours in the hope of influencing pay talks.

Sarkozy has sometimes tried to ingratiate himself with the protesters, but he said last week that locking up bosses was wrong and must stop. He worries the practice could spread, giving way to even greater violence as unemployment grows and with it the sense of injustice.

Violence certainly seems to be in the air and the fractious mood was further demonstrated by a film that appeared on the internet last week showing a group of hooded immigrant youths beating up a boy on a bus.

The driver does nothing as the victim is punched and kicked by assailants shouting “sale français” – “dirty Frenchman”.

A policeman has come under investigation for posting the film on the internet. It has fuelled anger on the far right, which blames a dramatic rise in violent crime on immigrant youths from the suburbs.

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