Bangladesh, Sept. 12 -- Britain's long-running struggle to control irregular migration across the English Channel is entering a potentially more dangerous phase. While the number of migrants arriving in small boats has reportedly fallen by more than 40 percent compared with the same period last year, the political and social tensions surrounding migration have intensified.

The latest warning signs have come not from the migrants crossing the Channel, but from organized far-right activists who have taken to the streets in increasingly confrontational ways.

Over the weekend, roads were blocked in Portsmouth after a boat carrying around 140 migrants arrived there. The incident followed similar disruption around the Port of Dover, where gr...