Prime minister Boris Johnson spoke to Jersey Chief Minister Senator John Le Fondre and External Affairs Minister Ian Gorst on Wednesday, and “underlined his unwavering support” for the island.
Dozens of French boats arrived at the harbour on Thursday morning, with some crews setting off flares during the so far peaceful protest, according to the Jersey Evening Post.
Paris has warned it could cut off power to the island, which receives 95% of its electricity from France through three undersea cables, in retaliation for the fallout.
A Ministry of Defence spokesman said: “HMS Severn and HMS Tamar are deploying to Jersey to conduct maritime security patrols.