Andrew Wallis, CEO of Unseen, a charity which supports victims of slavery and human trafficking, says three women discovered living in a house in Lambeth, south London, are among thousands of victims likely to be enslaved in the UK.
He estimated there could be as many as 5,000 people being kept in homes against their will.
Enslaved: Three women were rescued from a house in the London Borough of Lambeth after being held captive for more than 30 years. Charity Unseen says number of people held captive in UK could be more than 5,000
Mr Wallis toldThe Sunmosthuman trafficking was to force people into the sex industry but victimsare also forced to work either on domestic chores or by committing crimes.
He added: 'One of the women rescued this week was Irish, one Malaysian and another was born into slavery here. She has known nothing else for 30 years.
'People might ask why they don't just leave. But these people are abused and live in fear. They trust no one.'
A worrying trend is the amount of people brought to the UK for organ harvesting.
He added: 'A seven-year-old Somali girl was brought into the UK with the sole purpose of having her organs harvested.'
The three women rescued from a life of slavery in London this week had been held for at least 30 years.
A 30-year-old British woman, a 57-year-old Irish woman and a 69-year-old Malaysian woman were found after the Irish woman called a charity in a 'very distressed state'.
It has been claimed the couple suspected of keeping them captive used cult-like techniques to brainwash their victims.
Sources said the women were occasionally allowed out on their own to run errands but it is believed the trio are suffering from Stockholm syndrome, a psychological state in which hostages express empathy towards their kidnappers.
Police would not say whether other public bodies, such as social services, education authorities or hospitals, had had contact with the victims while they were captives.
Officers also refused to disclose whether any of the victims are related to each other or to the suspects, and whether the youngest victim – who is said to have spent her entire life in servitude – had been to school or her birth registered.
Police do not believe the case is one of sexual exploitation or human trafficking.
Slavery: The Lambeth case is just the 'tip of the iceberg' according to CEO Andrew Wallis who says traffickers treat people as a commodity. Metropolitan Police say of the women in Lambeth phoned the Freedom charity
The details emerged as detectives revealed the two suspects arrested over the case were known to police and had been detained in the 1970s.
They also said the pair, both foreign, are being investigated over unspecified immigration offences as well as allegations relating to slavery.
The arrested pair were released on bail on conditions that include a stipulation they are not permitted to return to their home in the borough of Lambeth where the victims were rescued from last month.
A police search of the address, believed to be in Brixton, took 12 hours. Officers seized 55 bags of evidence containing more than 2,500 exhibits.
Mr Wallis added: 'As this case clearly shows, slavery is a hidden crime. It’s a crime that is happening behind closed doors in the UK, but it is clearly happening.
Detective Inspector Kevin Hyland speaks to the press outside New Scotland Yard after three women were rescued from a Lambeth house. Andrew Wallis from Unseen says slavery is hidden behind closed doors
'The shackles are psychological what was holding them was fear and coercion and possible threats or actual violence against them.'
Mr Wallis, whose charity provides care to victims of human trafficking through its secure accommodation and resettlement project, said they are continually trying to raise awareness of slavery in the UK.
'We welcome the Home Secretary's determination to bring about the Modern Slavery Act as this is a step in the right direction, but as this news shows we need to do more.'
Co-founder of Unseen Kate Garbers said: 'In our experience survivors of human trafficking who have been through such trauma need long term care.
TIMELINE: HOW THE WOMEN WERE FOUND AND SAVED FROM 'SLAVERY'
October 18 - The Irish victim, 57, contacts Freedom Charity after seeing its founder on TV. She was 'distraught' on the phone and said she had been held captive for 30 years with two others. She was also said to mention her 'friend' who was being refused medical help after suffering a suspected stroke.
October 25 - She and the youngest victim, 30, meet the charity and police at a secret location before heading back to rescue the Malaysian woman, 69. They are taken to a 'place of safety.
November 21 - Foreign couple, both 67, are arrested on suspicion of immigration offences as well as slavery offences. They are bailed until January.
'It is not just the immediate support, but the on-going help that is essential to starting the road to recovery. These women have been through so much and there is no quick fix.
'This is a long and traumatic process, but there is hope at the end.'
Frank Field, chairman of the Modern Slavery Bill evidence review, said criminal gangs were making 'huge sums of money'.
Speaking to BBC Breakfast, Mr Field said many victims who escape have no way of communicating because they speak little or no English and often come from countries where they are 'deeply suspicious' of the police.
Cases of slavery around Britain have hit headlines in the past as the Serious Organised Crime Agency estimate there to be 2,255 potential victims last year in the UK.
An Irish traveller father and his son who forced destitute men to be their slaves were jailed for 13 years in May this year.
Tommy Connors Senior, 53, was jailed for eight years and his son Patrick, 21, for five years at Luton Crown Court.
The pair, from the Greenacres site in Little Billington, Leighton Buzzard, had been convicted last July of servitude, compulsory labour and assault charges after a trial at the court.
They preyed on vulnerable, homeless people who had drink or drug dependencies.
Sisters Bo, 46 and Yan Li, 43, were jailed in 2009 for laundering cash, linked to a human trafficking operation which claimed the lives of 23 cockle pickers at Morecambe Bay in Lancashire in 2004.
The Morecambe Bay disaster in 2004 saw 23 Chinese immigrants working for criminal gangmasters drown while cockle picking after they were trapped by the rising tide.
The deaths of the men and women - aged between 18 and 45 - exposed the illegal practices of gangmasters who exploit vulnerable migrant workers for cheap labour.
All of the victims had been illegal immigrants, some of whom had only been in the UK for a few months before the tragedy.
The man who sent them out on to the sands in February 2004 - gangmaster Lin Liang Ren - was later given a 14-year prison sentence for manslaughter.