A far-right activist known for organizing anti-immigrant rallies in Britain was arrested on Wednesday after he shared a video of himself slashing an inflatable dinghy in the English Channel while a person was on board.

A British police force, the Hampshire and Isle of Wight Constabulary, said in a statement that it had arrested a 37-year-old man. It did not further identify him, in line with British policing rules on not naming suspects who have not been charged.

But the man, Daniel Thomas, streamed a video on YouTube on Wednesday evening that appeared to show the arrest, at a gas station.

In a statement on Thursday, the police force said it had arrested the man on suspicion of several crimes, including destroying a ship or endangering its safety, and of criminal damage with intent to endanger life.

The arrest came after Mr. Thomas, who uses the name Danny Tommo, shared a video of himself in the English Channel pursuing a boat carrying migrants from France to Britain.

Mr. Thomas has espoused extremist views against migration and urged his followers to rally at ports and other sites housing newly arrived asylum seekers. In 2016, he was sentenced to two years in custody for an attempted kidnapping.

In June, Mr. Thomas said he had started a group, Patriot Platform, to channel anti-migration sentiment. He has claimed credit for recruiting protesters to gather recently in Dover and Portsmouth, where hundreds of masked men dressed in black blocked roads and chanted “Stop the boats!”

This month, Britain’s home secretary, Shabana Mahmood, described Mr. Thomas as an “outright racist.”

In the video filmed at sea, Mr. Thomas could be heard saying, “You’re on English territory. This is England,” before slashing the dinghy with a blade. No migrants were on the boat, but an emergency responder was aboard.

“You’ve got time to get off the boat,” Mr. Thomas shouted at the worker.