Britain’s government has condemned as “thuggish” hundreds of demonstrators who blocked roads vowing to prevent asylum seekers leaving the southern English city of Portsmouth after they arrived by small boat.

The protest last night was the second significant anti-migrant demonstration of the weekend after large crowds of masked men blocked access to the Port of Dover on Saturday.

“We condemn the intimidating and thuggish behaviour we saw in Portsmouth last night,” a spokesperson for the UK interior ministry, known as the Home Office, said in a statement.

“The right to peaceful protest is fundamental to our democracy but it must never cross a line into disorder.”

Social media footage showed the demonstrators, many dressed in black and with their faces covered, squaring up to police officers carrying riot shields.

The police officers had formed a security cordon around buses that were waiting to take the asylum seekers to a processing centre. The migrants were successfully transported, officials said, likely to the Manston arrivals and processing centre in Kent.

Earlier, French authorities had reported that a vessel carrying 140 people had departed Baie de Seine in Normandy, heading for England’s southern coast.

Arrivals of small boats in the county of Hampshire, where Portsmouth is situated, are extremely rare.

The vessels usually arrive further east in Kent, where the distance across the Channel between the French and British coasts is shorter.

England’s south coast is not prepared for the arrival of migrants, and ministers will have a “significant issue” if people traffickers shift their routes further west, Hampshire and Isle of Wight police and crime commissioner Donna Jones said.

Ms Jones warned that places such as Portsmouth are “not set up” for the arrival of migrants.

She told the BBC’s Today programme: “We have hundreds of miles of coastline across southern England and if Dover is no longer the destination of choice, and instead there is going to be a spread across southern England, this is a significant issue for the Government.

“My concern now, as a police and crime commissioner, is that we don’t have this repeated.”

Local Conservative MP Joe Robertson said in a post on X: “Extremely concerning to see an illegal migrant crossing this far west.

“We need to know exactly what happened and if new routes are being used for mega-dinghies by people smugglers.”

Livestreaming while standing in the sea at Eastney beach, Daniel Thomas, known as Danny Tommo – an associate of right-wing activist Tommy Robinson – said: “Roads are all blocked, they are never going to be able to leave here.”

He said: “It was only yesterday (at the protests in Dover) when we warned them that we will not accept this any more, and that this is no longer an option to tell us that the boat numbers are down.

“This isn’t about the numbers being down … this is about understanding that this has to come to an end now.”

The UK has been grappling with how to curb the perilous journeys, which have seen tens of thousands of asylum seekers arriving annually on the shores of southeast England in recent years.

The issue has spurred support for the hard-right Reform UK party.

The Home Office said last week that the number of crossings in August had fallen to their lowest level since records began in 2018, with migrant arrivals also at their lowest number since 2020.

But in recent months authorities have reported an increase in the number of passengers travelling per boat.

According to Home Office data, 16,513 migrants have crossed the Channel in small boats since the beginning of the year.

This is a tiny fraction of the overall number of people seeking every year to move to Britain. The vast majority arrive via legal routes, government data shows.