Staff who work in airport coffee shops are being trained to spot potential victims of trafficking, a senior clergyman has revealed.
Cardinal Vincent Nichols, head of the Catholic Church in England and Wales, said victims are being trafficked into the country by criminal gangs and disappearing into modern slavery.
Many are working in fisheries, farms and car washes up and down the country.
Once "underground" it is difficult to find and help them, so training for staff at Britain's airports in how to spot potential victims is crucial, he said.
The Modern Slavery Act was passed last year and introduced a life sentence for those found guilty of the crime.
Cardinal Nichols, a vocal supporter of the Act, has made tackling modern slavery one of his focuses.
Inspired by a group of nuns who worked with the Metropolitan Police in helping women trafficked to London and forced into prostitution, he has set up the Santa Marta group which brings clergy and police chiefs from around the world together to tackle modern slavery.
Nichols explained that a training programme has been started for "people who work in the coffee bars in the airports".
He said: "Often what happens is that people arrive, they come off the planes, they sit down for a cup of coffee and then their passports are taken off them."
He said this is "the beginning of the vice" that restricts the ability of victims to move around and get help.
Training staff in noticing when people arrive in Britain looking ill at ease and nervous - potential signs of trafficking - could help identify victims, and the criminal gangs bringing them in, the cardinal said.
He said: "It is trying to develop eyes and ears to see at these crucial moments, because once they have gone underground then and they are difficult to find until somebody gets out and talks."