The MP responsible for collecting evidence on slavery in modern Britain ahead of a new criminal bill has described the case of three women rescued in Lambeth, south London, from decades of forced servitude as just the "tip of a rather large iceberg".

Frank Field, who is chairman of the Modern Slavery Bill evidence review, said that people were being forced to beg, work as domestic slaves and in factories after being trafficked into the UK, with criminal gangs making huge sums of money from slaves' sale and exploitation.

"We've had this example of domestic slavery but people are being imported to work, almost for nothing, in industry," he told BBC Breakfast.

"We've got begging gangs being developed, with people being imported. And of course we've got the whole question of how children are being imported to work. It's a whole range of issues we've got to wake up to."

He said that many who managed to escape spoke no English, and came from cultures where people are "deeply suspicious" of police.

Andrew Wallis, CEO of Unseen, a charity that helps victims of trafficking, said that as many as 5,000 people could be enslaved in Britain.

He said that many were forced to work as prostitutes, and some were being brought into the country for 'organ harvesting', in which their organs are surgically removed and sold.

Field, who is also vice-chairman of the Human Trafficking Foundation, said that the scale of the problem was being exposed as more successful investigations were conducted.

"If you think where other countries have started to be serious about this, the numbers have risen sharply," he said.

"I would have thought it's safe to act on the assumption that the examples we've had in the last few months are the tip of a rather large iceberg."

The new bill is expected to introduce life sentences for enslaving, and create the role of anti-slavery commissioner, who will direct efforts to combat the problem.

"It's so shocking to just be talking to people who have been through this," the Labour MP for Birkenhead said.

"It's incredibly brave that people have been able to talk about it. They themselves say the one thing they want from the bill above all others is a champion, a spokesman," he said.

The three women, aged 57, 30, and 69, are currently being cared for by authorities after allegedly being held in captivity at an address in Lambeth, south-west London, for decades.

They were freed when the 57-year-old telephoned the charity Freedom Matters, who worked with police to help them escape.

A couple, both aged 67, were arrested and subsequently bailed.