Twenty - one suspected migrants were intercepted off the coast of France on Tuesday morning.
Nine people crammed into a boat called for help after their engine failed near Calais just before 5am.
Less than two hours later, a second boat with 12 on board, including two children, was intercepted by French authorities 12 miles west of Boulogne.
Two of those on board were treated for hypothermia.
Last week, three men were arrested following the discovery of a group of suspected migrants on a Kent beach.