LONDON — Day after day, news reports in Britain prominently feature migrants making the perilous trip across the English Channel in small boats, including a dozen who landed on Monday. Headlines and anti-immigration politicians call it a crisis, and the cabinet member in charge of migration policy has labeled it a “major incident” fueled by criminal gangs.

The total number of people, primarily from Iran, who have made the journey and requested asylum since early November is only about 240, in a country that has averaged about 25,000 asylum applicants per year over the last decade.

What is new is that they are regularly smuggled into Britain by boat — which used to be fairly rare — supplying jarring pictures of people being pulled from foundering little craft in rough seas, or being taken into custody on beaches.

And it comes at a tense moment in the nation’s politics, as Prime Minister Theresa May tries to arrange a divorce from the European Union — a process, known as Brexit, that has largely been driven by anxiety over immigration — while fending off calls from Brexit opponents for a second referendum on the matter.