Panorama traced the family of one child beggar back to Romania
You can see them on London's Oxford Street - day in, day out - young children begging.
For months, Panorama filmed them as they worked the streets during last winter's snow, sleet and rain. The footage - more than 100 hours of it - is like watching Oliver Twist for the 21st Century.
One little girl we followed, who we called "Alice", looked to be no more than four-years-old, yet she was experienced in begging; by turns, innocent, desperate, persistent, wheedling.
The little girl, wearing a white headscarf, used a telephone box as a toilet and scavenged for food from McDonalds as she begged in all weathers.
One restaurant owner in the area said that some child beggars make £500 a day. For her part, Alice handed every last penny to a minder, a young woman who looked to be in her late teens or early 20s.
Outside the Regent's Park Mosque, we filmed a team of women controlling several children, including a little boy of four, who we called "Lou".
They targeted worshippers from the mosque as they left Friday prayers.
We tracked "Lou" and his handlers as they took the bus home to a rented house in Ilford in Essex where a BMW X5 sat in the drive.
Over the course of almost a year, all of the child-begging teams working the streets of London which were investigated by Panorama turned out to be Gypsies from Romania.
Despite wearing modest clothing and headscarves and targeting the mosque and areas popular with tourists from the Gulf states, none were Muslim.
This is modern day slavery. How does a four-year-old child consent to be exploited?
Bernie Gravett, former Met Police Supt
Gypsies - also known as Roma - are Europe's largest ethnic minority, and the poorest. Racism against them in Romania and across Europe is rife.
Christine Beddoe, UK director of ECPAT (End Child Prostitution, Child Pornography and Trafficking), said forcing them to work the streets of London is denying them their childhood.
"It means that they are denied an education, they'll have nutrition issues, health issues," she said. "They'll also grow up believing that this is the only way, or the normal way, of earning a living."
In Britain, the police often stop the begging teams on the streets, but generally just take their details and let them go. Police say they fear that poverty has made Gypsies vulnerable to exploitation from criminal gangs within their own community.
They say they are working hard to combat the gangs driving the child begging business in Britain.
Former Metropolitan Police Supt Bernie Gravett led Operation Golf, which targeted the people behind the child beggars.
"This is modern day slavery. How does a four-year-old child consent to be exploited? They won't know that it's criminal to beg on the streets of the UK. They are kids."
Mr Gravett and his colleague Ch Insp Colin Carswell took part in a joint British-Romanian police operation, which arrested 26 alleged child traffickers from Tanderei in the south of Romania.
Child begging on London's streets
The accused, who were imprisoned for months but have since been released, denied any wrong-doing. The case continues as two judges in Romania have sent the case back to the prosecution but in the meantime the accused cannot leave the country.
In Britain, the police disrupted the gangs by targeting them for benefit fraud. Nine people, eight of them Romanian Gypsies, went to prison earlier this year for a total of 10 years for cheating £800,000 worth of benefits.
Romanians are not ordinarily entitled to UK state benefits, but police say that crime gangs have proved adept at getting around the rules using forged documents.
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John Sweeney presents Panorama: Britain's Child Beggars
BBC One, Wednesday, 19 October at 9pm then available in the UK on the
Ch Insp Carswell said one gang that was running children as beggars said the gang had pegged the earning potential of a single child in London at close to £100,000 a year between begging, stealing and being used for benefit fraud.
In the town of Tanderei, which is dotted with luxury villas, some of which police suspect have been paid for with the money begged on the streets of Europe, I met Petrica Dragusin, one of the men arrested on suspicion of child trafficking in the sweep in Romania as part of Operation Golf.
He told me bluntly that his entire town knows how to work Britain's benefit system.
"The blame is with the British state, which gives them a lot of money. They have lots of children, seven, eight or 10 children, and if they have many children they build a villa."
The sums he cites are staggering.
"Some collect £10,000, £12,000, £13,000 a month - they have three or four of five sets of benefits."
At the house in Ilford where we tracked "Lou" from his days spent begging near the Regent's Park Mosque, we filmed a series of children and adults coming and going, among them Ioan Rostas, his wife Stela and their daughter, Vandana, who we have been told has been investigated for benefit fraud.
We then tracked the Rostas family back to Huedin in the north of Romania, where local land registry documents show that Ioan Rostas owns two houses, a luxury villa on the main road and a smaller house on a sidestreet.
It was outside the smaller home that we encountered the same BMW X5 that has been parked outside the family's rented home in Ilford.
We also spotted little "Lou" at home in Romania.
And the little girl we called "Alice"?
Some of those filmed denied accusations of begging in London
From Oxford Street, we tracked her and her minder as they headed to Paddington station to catch a commuter train home after a long day on the streets of London. They lived in a rented home in Slough.
We found that her young minder was in fact her mother, Denisa Mazarache, and that they came from Fetesti in southern Romania.
In Fetesti, I knocked on the door of Denisa Mazarache's registered address, a recently built bungalow with a large front garden - not a luxury villa, but a significant improvement on the wooden shacks that the poorest of Romania's Gypsies are living in.
A man at the house angrily denied all knowledge of Denisa Mazarache.
At another house owned by a family member, I met Denisa herself.
She spoke in English and admitted to having begged in London: "I'm sorry. Because I don't have money to travel, to take one ticket, food."
I asked her about "Alice" and she said that she was going to nursery. "My children go to school and I've got a job."
She said they had left London a year ago and was no longer begging. But she was lying, we had filmed her less than two months earlier, begging on London's streets.
Panorama: Britain's Child Beggars, BBC One, Wednesday, 19 October at 2100BST then available in the UK on theBBC iPlayer
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