Traffickers shifting destinations along England’s south coast could present a new challenge in tackling the small boat crisis, an expert has warned.

Hundreds of masked demonstrators were in a standoff with police in Portsmouth overnight on Monday as they vowed to prevent migrants leaving after they arrived in a small boat.

The dinghy, reported to be carrying some 140 migrants, is thought to have made one of the longest journeys of any small boat and landings as far west as Hampshire are rare.

It was met by lifeboats from the Isle of Wight when it reached UK waters, having set off from the Cherbourg area.

Those protesting blocked roads for hours and were vowing to stay all night. Their behaviour was condemned by the government as “intimidating and thuggish”.

Coaches were able to leave in the early hours of Monday taking all of those brought ashore to a location for processing in the usual way, likely to be the Manston arrivals centre in Kent, where the vast majority of arrivals are processed.

According to Mihnea Cuibus, senior researcher at the University of Oxford’s Migration Observatory, the “ongoing cat-and-mouse dynamic between the authorities and smugglers” could result in the latter shifting their desired destinations across England’s coast to avoid the frequently-used and patrolled Calais to Dover route – the shortest route from France to England.

He told : “The second you see a surge in enforcement – more patrols, essentially the authorities making it harder for migrants and boats to leave from one particular area – then you see that relatively immediate adaptation, especially coming from the gangs, essentially to try to find ways around it.

“It's much harder to leave by boat from around the Calais area because of all of the patrols, drones in the air, and more boots on the ground, so they're just trying to find ways to avoid that.”

Mr Cuibus believes it is “too early to tell” whether small boats arriving on other parts of the English coast will become a big issue, but much of the nation’s infrastructure for processing migrants who cross the Channel has been built in Manston, around 20 miles from Dover.

He added: “What we saw with the arrival in Portsmouth is a shift in the sense that not only did the boat depart from further south, but we're also seeing it head over to the UK and cross the Channel through that longer route.

“It's very much an open question if and to what extent we'll see more of that in the coming months.”

Donna Jones, Conservative police and crime commissioner for Hampshire and Isle of Wight, said that places such as Portsmouth are “not set up” for the arrival of migrants after hundreds of black-clad demonstrators entered into a standoff with police in the city overnight, as they vowed to prevent migrants leaving after they arrived in a small boat.

Following the protests, Ms Jones said the government has “invested heavily into Dover” to deal with the situation, but other places along the coastline lack vital equivalent infrastructure if small boats are to arrive there.

She told the BBC’s 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.”

Portsmouth’s Liberal Democrat council leader Steve Pitt said the Home Office has “serious questions to answer” after an “unsuitable” location was chosen to disembark the RNLI boats on Sunday.

“The council wasn’t asked about the decision to land the lifeboats in Portsmouth”, he said. “This was entirely a decision taken by UK Border Force, the Maritime and Coastguard Agency and the Home Office.

“It was a completely unsuitable location to bring the boats ashore, this entire situation was avoidable and has brought needless disruption to our city”.

However, Mr Cuibus said that it is action on the French side that's pushing boats to be further away from Dover.

Asked whether different points of arrival into the UK will present a new challenge to the government, he said: “Yes, to a certain extent.

“That's exactly the challenge and the point in terms of making it harder for the authorities.

“Right now, a lot of the focus and the reactions we're seeing are connected not with what's going on on the UK side, but what's happening on the French coast”, he explained.

“In theory, this longer route across the Channel is most likely a response to what's happening on the French coast.

“The question is whether there is an incentive on the UK side as well to arrive in a different area compared to the area surrounding Dover.

“Legally, it shouldn't make much of a difference. When it comes to small boat arrivals, the purpose is not to evade the authorities once you're in British waters, because the vast majority of these people are happy to declare themselves to the authorities in order to claim asylum upon arrival.”

Following the demonstration, Hampshire and Isle of Wight Constabulary have launched an investigation into potential assaults and criminal damage.

Official vehicles were damaged and a handful of police officers injured after demonstrators blocked the road leading away from the RNLI Portsmouth Lifeboat Station at Eastney Marina, with photos showing police carrying riot shields forming a line and protecting a number of coaches that were parked up.

A Home Office spokesperson said: “We condemn the intimidating and thuggish behaviour we saw in Portsmouth last night.

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

“We thank the emergency services who safely managed this situation.

“This Government is doing the hard and necessary work of bearing down on small boats crossings, with the lowest number of June to August arrivals since 2020.”