Hampshire police detained the 37-year-old on suspicion of criminal damage with intent to endanger life after he filmed himself cutting a migrant dinghy's side while a rescuer was aboard.
Home Secretary Shabana Mahmood called the lapses "not acceptable" after consecutive undetected landings on the English coast.
Authorities say the vessel lacked safety equipment and was taking on water before being intercepted by Border Force officers.
A UK agency says stepped-up enforcement is behind a recent decline in Channel crossings, though it notes other factors, including events in the Middle East, could also be contributing.
Reform UK leader Nigel Farage has unveiled a deal with France's National Rally party addressing Channel crossings, with Reform saying it would deploy the Royal Navy to intercept boats and return migrants to France if it wins power, according to the BBC.