Natacha Bouchart, leader of the French coastal town from which many migrants have departed, condemned the UK government’s proposal to enlist the Royal Navy to stop boats reaching Britain.
“I say clearly, that it’s a declaration of maritime war since it is out of the question for naval ships to enter [French] territorial waters,” she told the Agence France-Presse news agency.
“I consider Boris Johnson’s pronouncements to be a provocation,” she added. “Therefore I appeal to Boris Johnson, saying you urgently need to calm down, and urgently need to change your methods of … dealing with migrants.”
It comes as a new YouGov poll found that 71 per cent of British adults backed the idea of the Royal Navy patrolling the English Channel to stop migrant crossings.
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The same survey also showed that 69 per cent of adults supported the RAF working with the Border Force in the Channel.
RAF search and rescue surveillance aircraft have been used in recent days, but the Royal Navy has yet to deploy vessels to the English Channel despite a request for assistance from home secretary Priti Patel.
The Calais mayor has echoed calls from refugee rights campaign groups in the UK in calling for Mr Johnson’s government to focus on creating safer, legal routes for asylum seekers.
Ms Bouchart said the French government should not “give in” to British requests for stronger border enforcement measures on the coast of France. “It’s only by standing firm that you achieve something.”
Earlier this week UK immigration minister Chris Philp said French officials had agreed to work on “joint operational plan” to make the English Channel “unviable” to migrants – but also said he could not discuss any “operational” details.
Ms Patel and her French counterpart Gérald Darmanin last month signed an agreement to establish a joint intelligence unit to tackle migrant traffickers.
A Ministry of Defence spokesperson said: “All capabilities provided have been in response to requests made by the Border Force. Defence continues to work with the Home Office to provide appropriate support, as needed.”