LONDON — The British government on Monday condemned the “intimidating and thuggish behavior” of anti-immigrant demonstrators who converged on a port in southern England where migrants were brought ashore after crossing the English Channel.

Hundreds of protesters, many dressed in dark clothing and wearing masks, faced off with police in Portsmouth late Sunday in an attempt to prevent lifeboats from bringing the migrants to land. They then tried to block buses carrying the new arrivals to a processing facility for asylum seekers.

“The right to peaceful protest is fundamental to our democracy, but it must never cross a line into disorder,” the government said in a statement.

The Portsmouth protest came a day after hundreds of masked anti-immigration protesters blocked roads leading to Britain’s busiest ferry port of Dover on Saturday, clogging traffic and disrupting travelers as well as cargo vehicles heading for France.

Both groups appeared to be led by Daniel Thomas, an ally of veteran far-right activist Stephen Yaxley-Lennon, better known as Tommy Robinson.

Successive U.K. governments have struggled to stop people — more than 40,000 last year — making the dangerous journey across one of the world’s busiest shipping lanes.

The issue has been depicted as a crisis by politicians including Nigel Farage of the hard-right party Reform UK, and has been used as a rallying point by anti-immigration activists.

Prime Minister Andy Burnham’s government says stepped-up law enforcement cooperation between Britain and France has helped reduce the number of people making the crossing so far this year by more than 40% compared with 2025.

The boat carrying about 140 people to Portsmouth had left early Sunday from Normandy, far west of the beaches near Calais where most departures have taken place — making it a much longer and riskier journey.

Britain’s Maritime and Coastguard Agency spokesperson said lifeboats, a coastguard helicopter and a plane were involved in the operation to bring the migrants to shore.