In Paris up to 40,000 demonstrators marched from Republique to Bastille and large turn-outs were reported in many other cities, including Marseilles, Toulouse, Rouen and Grenoble. Teaching unions postponed their own planned demonstration on educational issues to join the action.

Power-sharing deals made with the NF by five politicians from the centre-right UDF party will allow them to retain their presidencies of local councils, even though the Left won most votes in those regions in last month’s regional elections. President Chirac denounced the deals with the “racist and xenophobic party” in a nationwide broadcast.

Support for the NF, which won more than 15 per cent of the national vote, spreads across all social groups but was strongest among those including shopkeepers and small business people. It won the single-biggest working-class and unemployed vote. Geographically it is concentrated mostly in the south of France, the North, Alsace and Paris.

It controls four town councils, all in south-east France. So far the councils have banned disapproved books from public libraries, denied foreigners any pension rights and withdrawn alternatives to pork which are usually provided for Muslim and Jewish pupils in school canteens.

Last week tens of thousands of primary pupils and their teachers took part in the National Week Against Racism in 60 departements.

Prominent among the Paris crowds on Saturday were young people, including many secondary pupils and university students. Clapping and shouting slogans, they ambled along the sunny boulevards, some pausing only to roll giant joints which they smoked as a gesture to show their freedom in what they called “this corrupt society that spawns fascists”.

Matteo, 15, said he was marching “because this is our future, these Nazis want to take over our lives and who knows what will happen if we don’t all react? Shall we really be able to say in 20 years that we couldn’t see it coming?” David, also 15, said: “Even though we might not be able to change anything today, we want to show the NF that we will be here when things really matter.”

Also prominent were those aged over 50, many of them active during the tumultuous “events” of 1968, the 30th anniversary of which is now being commemorated.

In March that year students of Paris university at Nanterre staged strikes and occupations, initially in protest against working conditions, but which soon led to a nationwide questioning of French society.

The country was paralysed as workers and unions joined forces with the students and stopped working. The events culminated in May with riots during which students memorably used the paving stones of Paris to hurl at the police who were tear-gassing them.

Only significant concessions from the Government saved it from being toppled by the protests.