This human vending machine highlights the reality of modern slavery

On a crisp morning in central London, a large vending machine has caught the attention of shoppers and commuters.

Behind the glass sits a bruised and weary slave ready to dispense fresh tomatoes, lemons, avocados and eggs at the touch of a button.

The confrontational campaign, which used actors and a custom-built vending machine, highlights the plight of the estimated 136,000 people in Britain currently trapped in slavery.

"As consumers we're often concerned about the provenance of our food. But many of us are unaware there may be human costs involved in bringing food to our tables here in the UK," said Cristina Talens, a researcher from the University of Hull in northern England.

"The areas of our lives affected by modern-day slavery ... are widespread with forced labour existing in the hospitality, domestic, beauty and construction industries to name a few," said Talens, who assesses slavery risks in businesses.

Britain's 2015 Modern Slavery Act requires firms whose turnover exceeds 36 million pounds ($46 million) to produce an annual statement detailing the actions they have taken to combat slavery in their operations, but does not include public bodies.

Just over half of the about 19,000 companies required to comply with the law have issued statements to date, according to Transparency in the Supply Chain (TISC) - a public database.

Raising awareness among consumers can also be a challenge.

In a report on Monday, a third of British adults quizzed in a YouGov poll were not aware that slaves were used to produce fresh foods, according to research from the Wilberforce Institute at Hull University, which commissioned the survey and organised the street campaign.

Aral, 20, one of the actors inside the vending machine, said he was not aware of the issue before he joined the campaign.

"I had no idea that it was happening in the UK, I thought slavery was something that happened a hundred years ago," he added and declined to reveal his full name for privacy.

One in five Britons surveyed did not believe that slavery happens in the country now, the report added, with one in 10 saying that though slavery existed in the past, it no longer happens today.

Yet more than 40 million people are estimated to be trapped as slaves in forced labour and forced marriages, most of them women and girls, according to the International Labour Organization (ILO) and rights group Walk Free Foundation.

Nearly 25 million work in factories, on construction sites, farms, fishing boats and as domestic or sex workers, says ILO.