France's Socialist Prime Minister Lionel Jospin has been dealt a severe blow, with the decision by the country's highest judicial authority that the central part of his self-government plan for the island of Corsica is illegal.

The nine judges who make up the Constitutional Council delivered their ruling Thursday night, after being invoked by right-wing members of parliament who are opposed to Mr Jospin's initiative to hand down limited legislative powers to the island's regional assembly.

Jospin: Overruled three times in a month

The council ruled that the most important clause in the Corsica devolution bill - which was voted through last month - was against the constitution, because only the National Assembly in Paris had the right to pass or amend laws.

Mr Jospin had proposed - after long negotiations with Corsican politicians, including nationalists - that the island's assembly should have a very limited power to adapt certain laws in local interests.

Other parts of the law, including the handing over of certain regulatory powers and the extension of Corsican language teaching, were accepted, though the council said the language must never become obligatory.

However it is clear to all that the core of the autonomy bill - wrestled through parliament after two years of often acrimonious negotiations - has been removed.

'Wise men'

Mr Jospin was putting a brave face on it Thursday evening, saying that the so-called Matignon process - named after his residence in Paris - was the only way forward to bring to an end the last 25 years of separatist violence.

But the council's ruling is hurting hard.

We have to ask questions about the legitimacy of the constitutional council Noel Mamere, Green Party

With elections only three months away - in which he is expected to stand against President Jacques Chirac - it is the third time in a month that the constitutional council has declared a key part of his legislative programme to be null and void.

In December the "wise men", as they are called in France, banned the government from raiding the social security budget to meet the cost of the reduced 35 hour week.

And only last Saturday they said that a law restricting the right of businesses to lay off staff in order to restructure was an attack on the "freedom of enterprise."

Co-habitation problems

It does not look good when three achievements he was hoping to campaign on have been emptied of meaning, and the right is making the most of it.

President Chirac's RPR party said it was sign of Mr Jospin's "obstinacy".

The left is putting it down to in-built right-wing bias in the constitutional council, which deputies say is making a mockery of the legislative process.

"We have to ask questions about the legitimacy of the constitutional council," said the Green party candidate in April's election Noel Mamere.

"It also shows the disastrous effects of co-habitation. The council is in effect the referee between the two leaders of our executive (Messrs Jospin and Chirac) and deciding what is good for France. I cannot accept that."

The Matignon process was the latest in a series of attempts by the government in Paris to find a solution to the problems of Corsica, which has been prey to a mixture of separatist and mafia-style violence for a quarter of a century.

And like all its predecessors, it looks like it is going precisely nowhere.