Riot police have begun to arrive in Calais as an anarchist group pledged to help illegal migrants ‘tear down border controls and make for Britain’.
More than 2,000 protesters are expected in the port next week for seven days of direct action.
The French arm of a group calling itself No Borders is advertising a ‘Freedom of Movement’ camp in the port.
It is calling on protesters from Britain and other European countries to join them in ‘tearing down borders.’
One anarchist, known only as Thierry, said: ‘Calais is a symbol of injustices committed against the world’s migrants.
‘The authorities are taking us very seriously. We intend to encourage migrants to ignore border controls and get over to Britain en masse.’
‘We’re prepared for the worst,’ said Jean-Philippe Joubert, a state prosecutor from nearby Boulogne.
‘Emergency magistrates will be mobilised to ensure that anyone causing trouble will be imprisoned immediately.
‘We don’t know exactly what this group intend to do, but we won’t take any chances.
‘Whatever happens, we are ready to react.’
Some 2,000 migrants are based in the Calais area, with many playing a regular game of cat and mouse with the police as they try to get to Britain by stowing away on lorries and trains.
There they will claim asylum or disappear into the black economy.
Although the French have pledged to tear down migrants camps in Calais itself, many believe Britain should accept all the migrants who want to go there.
Last month Natacha Bouchart, the mayor of Calais, said the UK’s lax asylum system and benefits culture had ‘imposed’ thousands of illegal migrants on her town.
In a blistering attack in which she also called for millions in compensation, Mrs Bouchart said the UK was entirely to blame for the those who use the port as a staging point.
Mrs Bouchart, a member of President Nicolas Sarkozy’s ruling UMP Party, even called for border controls to be lifted to allow all migrants to flood across the Channel at the earliest opportunity.
Such views are heartily supported by the militants organizing the ‘No Border’ demonstrations, which are set to run between June 23 and 29.
A Calais police spokesman added: ‘Extra officers are being drafted into Calais from a 100-mile radius in order to deal with a threat to public order posed by protesters.’
‘The reinforcements have already arrived, with the demonstrations due to start properly next week.’