Victims of modern slavery in Britain have spoken about being forced to work 19 hour days for little or no pay, beaten up and having their IDs taken from them, in a program by the UK's Channel 4 television.Due to be broadcast on Tuesday evening, The Modern British Slave Trade follows prosecutors as they investigate cases of labour exploitation, and interviews victims about the abuse they experienced.Filmed over two years, it details the story of Christopher Nicholls, whose skeletal remains were discovered in 2008, six years after he disappeared.He had been working for a traveller couple William and Mary Connors, who ran a business laying driveways and were jailed on forced labour convictions in 2012. They held Nicholls captive and physically abused him, according to another employee.Victims who worked for other members of the Connors family spoke about being hit with brooms or hosed with cold water naked in the middle of winter.One former worker, Mark Ovenden, said he was on the edge of destitution after losing his job in 2009 when he was recruited."I experienced some hardship, I started to feel very depressed," he told Channel 4.Offered a job with accommodation and three meals a day by one of the Connors family, he agreed.But once he arrived at their rural property, he found workers were living eight to a horsebox. His head was shaved, clothes taken and his phone and ID were confiscated."I was definitely kept a prisoner," he said. "It was made very clear that if... I was to try and leave the consequences would be very great."The program also interviews migrant workers, including a 16-year-old boy who was trafficked from Vietnam to work at a nail bar.There are an estimated 13,000 victims of forced labour, sexual exploitation and domestic servitude in Britain.In 2015 the UK passed tough anti-slavery legislation introducing life sentences for traffickers and forcing companies to disclose what they are doing to make sure their supply chains are free from slavery.Last week, two Polish brothers were jailed under Britain's modern slavery laws for stealing wages of around 18 other Poles they tricked with promises of work in the UK.The brothers seized their travel documents, credit cards and most of their wages and -- by sometimes threatening violence -- exerted total control over them, prosecutors said.