Workers at a Sony <6758.T> plant in southwestern France detained the chief executive of the Japanese group's French arm overnight to demand better layoff terms when their factory closes in April.

Workers had locked up the managers in the plant at Pontonx-sur-l'Adour late on Thursday and blocked the road to the site with tree trunks, local authorities said.

Union representatives said their action had been the only way to revive negotiations on layoff packages that were not generous enough.

We hope that this time our voices will be heard, unionist Patrick Hachaguer told Reuters by telephone as workers and the released managers boarded minibuses to go and resume talks at local government offices.

Tempers have been boiling over in France, hit like other countries around the world by a wave of factory closures and mass layoffs because of the global economic downturn.

Workers in a small northern town hurled eggs and insults at managers on Thursday to protest against the closure of their tire plant by German car parts group Continental that would eliminate 1,120 jobs.

At Pontonx-sur-l'Adour, the Sony plant which employs 311 workers is scheduled to close for good on April 17. Foucher's visit to the plant on Thursday was the last before closure.

Sony had considered converting the plant to make solar panels rather than magnetic components, but abandoned the plan, angering the workers who had hoped to keep their jobs.

Local authorities mediated to avoid a police intervention that would have further raised tensions.

(Reporting by Claude Canellas, writing by Estelle Shirbon; editing by Philippa Fletcher)

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