The anti-migrant protest group, which has staged balaclava-clad demonstrations in Dover and Portsmouth, is said to be considering taking out a vessel to confront would-be asylum seekers as they cross to Britain.
An undercover Sun on Sunday reporter at the Portsmouth protest last Sunday heard balaclava-clad members discussing the tactic.
It would likely involve the group taking a hired boat into international waters, potentially disrupting the busiest shipping lane in the world.
They may then attempt to turn a dinghy around and take it back to France or simply block it.
Border Force or the French fleet could have to intervene.
There is no suggestion group leader Daniel Thomas, known as Danny Tommo, is involved.
He has staged stunts including trips to Calais and Dunkirk beaches, and was banned from France after slashing ditched migrant dinghies.
A source said of the Channel plot: “The idea has been discussed.
“It’s an early-stage idea, but in the eyes of the activists, physically stopping a boat when the French and Home Office can’t do it would be a major moment.
“It could end in tragedy, but shows how furious these people are.”
Last Sunday, the launch of a migrant dinghy from Normandy sparked a flash protest in Portsmouth, where a volunteer RNLI lifeboat took 120 would-be asylum seekers to shore at Eastney Docks.
Their arrival was delayed for several hours by Tommo and balaclava-clad protesters who had a stand-off with Hampshire Police officers.
The migrants were eventually brought ashore for processing, but coaches taking them to Home Office sites in Dover were followed by far-right activists.
It came after a similar protest shut the Port of Dover last Saturday.
The group marched through the Kent town, chanting “Whose streets? Our streets” and “Stop the boats” as dozens of police officers followed.
The march prompted condemnation from across the political spectrum.
Reform UK leader Nigel Farage described the scenes as “disgusting” and said protesters should not be allowed to demonstrate while wearing balaclavas.