France and Britain vowed on Sunday that a cross-Channel migrant crisis was their "top priority" in a united front that belied simmering anger.

Heightened security has curbed the number of attempts by migrants in the port city of Calais trying to make it through the undersea Channel Tunnel to Britain, with only 400 bids on Saturday night, a police source said, compared to 2,000 earlier in the week.

About 3,000 people from Africa, the Middle East and Asia are camped in Calais hoping to smuggle themselves into Britain, and the costly crisis has strained ties across the Channel.