Britain’s National Crime Agency said a woman aged 23 and three men aged 64, 34 and 25 were taken into custody last week after they were picked up at addresses in London, Croydon and Leicester.

Three were arrested on suspicion of assisting unlawful immigration and appeared at Croydon Magistrates Court on April 23.

The 25-year-old man is wanted by the French authorities, who allege he was involved in people smuggling and drug offences. He will now face extradition proceedings.

Following the arrests, UK Home Secretary James Cleverly said a new agreement has been signed with Vietnamese authorities to crack down on illegal migration.

Investigators allege the group were involved in advertising illegal immigration into the UK in social media posts aimed at the Vietnamese community, charging migrants thousands of pounds to make the crossing.

The 64-year-old is believed to have acted as a driver, collecting migrants who arrived on small boats and on at least one occasion bringing them back to the Croydon address.

At the same time in France, another 12 individuals have been arrested in the Paris area, suspected of being linked to the same people smuggling network.

UK Home Secretary James Cleverly said: “We are using every possible lever at our disposal to crack down on people smugglers and break their supply chains. Just last week, we signed a new agreement with Vietnam, strengthening our cooperation on illegal migration.

“Together with law enforcement agencies such as the NCA, our French partners, and other countries like Vietnam, we are committed to dismantling the criminal gangs who are trying to turn a profit by abusing our borders.

“This operation is a prime example of that partnership working in action.”

National Crime Agency Director of Threat Leadership Chris Farrimond added: “People smuggling via small boats is extremely dangerous and the safety of those making the journey is of no concern for criminal groups who are exploiting them for profit.

“As well the high-risk method of transport, entering under these clandestine means automatically puts these people under increased risk of being forced into exploitation and debt bondage by these groups. Migrants are often sold a dream of a better life and access to well-paid employment in the UK but this is not the reality.

“Vietnamese nationals now make up a large number of those we see arriving on small boats. We allege this group were advertising their crossing services on social media to encourage others from their country to make the same treacherous journey.

“The NCA is continuing our work with partners and has had thousands of social media pages and posts advertising organised immigration crime services removed from platforms.

“These arrests were possible thanks to our close working with the CPS and the French authorities who have arrested a number of people they believe are linked to this group in France.

“Tackling organised immigration crime is a priority for the National Crime Agency and our investigation continues to target people smugglers both in the UK and overseas at every step of the route.”