Eight men were being held by detectives last night after more than 200 police officers carried out a series of dawn raids to smash a people smuggling network thought to be among the largest in Europe.

Several alleged senior members of the gang were among those held in the raids early yesterday at 12 houses in London and one in Boston, Lincolnshire.

Senior officers considered the network to be one of the largest people-trafficking gangs they have encountered.

The eight suspected members of the smuggling network were being held on suspicion of facilitating human smuggling.

It is believed the group, a pan-European organisation, could be responsible for smuggling thousands of mainly Turkish Kurds into the UK illegally in the past few years.

Senior sources said it was impossible to say exactly how many people the network had brought into Britain, but it could potentially be in the low tens of thousands.

The raids were a culmination of a two-year Scotland Yard investigation, codenamed Bluesky, which involved the co-operation of law enforcement agencies in five other European countries.

A further 11 people, including former asylum seekers, were also arrested.

Two women were arrested on suspicion of interfering with the inquiry.

Six people were held on suspicion of immigration offences, two people were arrested on suspicion of theft and a man was held on suspicion of money laundering.

All 19 of those held yesterday were still being questioned by detectives last night.

In London, raids were carried out at houses and business premises in Enfield, Bexleyheath, Barnet, Haringey, Tower Hamlets, Hackney and Hammersmith.

Specialist officers also carried out extensive searches of the properties and a substantial amount of money was recovered.

A dark blue Mercedes saloon car was also searched by forensic officers at one of the houses.

Scotland Yard Assistant Commissioner Tarique Ghaffur, head of the Specialist Crime Directorate, said: "We have dismantled a huge organised criminal network of human smuggling."

He added that the raids were targeted at those "right at the top of this network".

The gang is thought to have lured thousands of economic migrants to Britain with the promise of a better life.

Police are unsure exactly how long it has been operating, but it is understood the investigation stretches as far back as three years.

It is alleged to have operated by charging people between £3,000 and £5,000 to be smuggled in groups of up to 20 at a time from Turkey, across mainland Europe to the continent's northern coastal ports.

"Once there, they waited in safe houses until the time was right for them to be smuggled into Britain.

Once in Britain, most have simply been absorbed into north London's Turkish community, working in low-paid menial jobs.

It is thought the smuggling ring could have made tens of millions of pounds, some of which has been invested in businesses such as cafes and snooker halls.

Law enforcement officials from France, Italy, Holland, Belgium and Denmark, and Europol have all contributed to the investigation.

Detective Chief Superintendent Bill Skelly said the network was the largest people smuggling ring Scotland Yard had encountered and that the operation was the most significant mounted so far to tackle organised immigration crime in London.