PARIS - A wave of "boss-nappings" and sit-ins by workers faced with losing their jobs has caught France's Government wrong-footed and left its trade union movement struggling to channel anger building on the factory floor.

In seven weeks, executives at six firms, including the local subsidiaries of Sony, 3M and Caterpillar, have been detained by workers after they announced job cuts.

On March 31, riot police intervened to free tycoon Francois-Henri Pinault after shopworkers, incensed at plans to axe 1200 jobs from his retail and luxury chain PPR, blocked the billionaire in his taxi.

In Compiegne, north of Paris, the local offices of the prefecture - the highest authority of the state - were ransacked by workers from the Continental tyre plant, who then attacked the security post at the factory gates.

Last week, militant electricity workers cut off power to tens of thousands of people in the Paris region, including hospitals, for hours at a time by sabotaging local transformer stations. Half a dozen other factories around the country are being occupied or blockaded by workers.

"It is absolutely criminal. The word for it is hostage-taking ... These acts give France a catastrophic image in the business world," said Marcus Kerriou, co-manager of a car parts plant at Villemur-sur-Tarne, southwestern France, operated by Molex of the United States.

Kerriou was held for 26 hours with Molex's head of human resources after the plant announced 300 job cuts.

The pair were released after an exhausting night in which they had just two hours' sleep, paraded in front of the media and allowed to go to the toilet only under escort. They had to walk through a baying, jostling mob of around 100 workers to get out.

The rash of incidents has rattled the Government, spurring fears that the May 1 parades in France - a traditional show of strength by organised labour - could degenerate into riots.

"There is a risk of revolution," Dominique de Villepin, a former Prime Minister, said last week.

Prime Minister Francois Fillon has offered a verbal mix of warning and compassion but skirted the idea of a Thatcher-style crackdown, clearly believing this could inflame the situation.

That approach follows the line set down by President Nicolas Sarkozy.

Two days of nationwide strikes this year saw more than a million demonstrators take to the streets, prompting Sarkozy to set up a round table with unions where he agreed to measures designed to ease the pain of recession.

But the ferocity of the downturn caused a sudden wave of closures. The mood quickly radicalised, turning from strikes to sit-ins and then boss sequestration - and from the spontaneous to the organised.

Kerriou said his detention was orchestrated from outside the Molex plant, "given the professional spin-doctoring".

Detained bosses are usually held in their offices before being released unharmed after a few hours or a night.

Caterpillar has pressed charges for illegal detention and fired 22 workers involved in the sequestration. But in other cases, companies have agreed to new negotiations with the unions.

Mainstream unions and the Socialist and Communist parties find themselves having to catch up with sentiment on the shop floor, saying they understand the reasons for anger and despair but stopping short of endorsing violence. "We'd been trying to hold them [the workforce] back for five weeks, we just couldn't stop them," said Xavier Mathieu of the Communist-led CGT union after the rampage in Compiegne.

"The people ... here weren't vandals, but angry people, disgusted, on the brink of depression. All this talk of smashed windows and damaged computers, that's nothing compared with 1100 lives that are going to be wrecked by unemployment."

Seen from the outside, France is in a relatively favourable position in the global recession.

It avoided the property bubble that has so afflicted the US and British economies and is not so dependent on exports as Germany and Japan.

Its gross domestic product shrank by 1.2 per cent in the first quarter of this year compared with the same period last year, but that compares with a retraction of 1.6 per cent for the overall euro zone.

Sarkozy is pumping 26 billion ($60 billion) into the economy and led calls for curbs on executive pay and restrictions on financial traders.

But this has not saved France from the storm, especially in the northern rustbelt, where anyone who loses his job is potentially condemned to years of unemployment.

Adding to the sourness is the collapse of capitalist doctrine, headline-making scandals about executive pay and criticism that Sarkozy's help is directed more towards business chums than the working public.

It has sharpened the reflex for "direct action", a far-left tradition dating back to the 1789 French Revolution that critics say stokes a reputation for lawlessness which destroys jobs.

"The culture of equality is very strong in this country," said Jean-Claude Delgenes, head of a risk consultancy called Technologia.

"Because of the [economic] crisis, workers consider that the elite has failed. On top of that, they are being asked to pay for the mistakes of others by losing their job or being put on part-time working."