Criminal gangs from the British and Irish travelling community have been transporting vulnerable men abroad to work in an operation described as "modern slavery".

The victims are often homeless people picked off the street with drink or drug problems. An investigation by the BBC Ten O'Clock News and Radio 5 Live Breakfast found at least 32 victims.

According to the BBC, there have been confirmed cases in six European countries, including Sweden, Norway and Belgium, but the European Commission believes the problem is more widespread.

One man, who did not want to be named, said he arrived at the Swedish port of Malmo with two other homeless Britons. They worked 14-hour days for little pay and had to live in poor conditions. The man said they were too afraid of violence until the Swedish police offered them support.

"I've seen people threatened with pickaxes. I've seen people kicked, punched. I've nearly been pushed off a moving vehicle. It's very tense. You're waiting for the next thing to happen," he said.

Cecilia Malmstrom, European Commissioner for Home Affairs, told the BBC: "It's a horrible crime and it's modern slavery. They are using very vulnerable people and especially in hard economic times, people have lost work, nowhere to live, thrown out from families. We must act much stronger than we have done."

A Swedish report into human trafficking, published in 2010, found 26 incidents of non-sexual trafficking. It stated: "The victims do not usually report personally that they have been the subject of human trafficking because they often have no confidence in the authorities that administer justice and are afraid of acts of reprisal."

In December, seven people appeared at Luton Crown Court over slavery offences following a raid at a traveller site in Bedfordshire. They are charged with conspiring to hold a person in servitude and conspiracy to require a person to perform forced or compulsory labour, after a police operation at the Green Acres caravan site near Leighton Buzzard.

A Home Office spokesman said: "The Government is committed to tackling human trafficking and preventing the harm it causes to vulnerable members of our society.

"Our human trafficking strategy sets out how we are working with partners both at home and across Europe to enhance our intelligence and law enforcement capabilities so that we can prevent vulnerable people from becoming victims in the first place."