File picture: Independent Media

London - British police arrested 21 people on suspicion of involvement in human trafficking on Tuesday, saying their nationwide operation was one of the biggest so far against organized people smuggling.

The National Crime Agency said it had launched "a major operation targeting a suspected people smuggling, organized criminal network" in London, north-eastern and southern England.

"The operation is the latest phase of a year-long investigation, which has involved law enforcement colleagues in the UK and in Europe," the NCA said.

It said some 350 officers from the NCA and four regional police forces raided more than 20 properties in towns and cities including Middlesbrough, Hartlepool, Stockton, Newcastle, Hastings and London.

"This was probably the biggest operation the NCA have taken on within organized immigration crime," Mark Spoors, senior investigator for the NCA, said in a statement.

"We see this as a significant disruption within the UK against the organised people smuggling ring, which was predominantly operating out of Cleveland," Spoors said, referring to the north-eastern region that includes Middlesbrough, Hartlepool and Stockton.

The alleged offences include "complicit lorry drivers running form France into the UK," and the hiring of drivers from the Cleveland area to travel to France and collect migrants, he said.

The properties raided included car washes "linked to the organized crime group," Spoors added.

French, Belgian and Dutch police assisted with the investigation, said Tom Dowdall, the NCA's deputy director.