A paedophile exploited his friendship with a prominent politician to get a job which he then used to gain access to vulnerable children abroad.
Derek Slade, who set up a school in Asia and worked at one in Africa, stole a dead boy's identity to hide his past.
The findings are featured in a BBC documentary by journalist Roger Cook.
An Abuse of Trust is being screened almost 30 years after the veteran reporter first exposed Slade's sadistic activities at a school in Suffolk.
The revelations about the headmaster's excessive use of violence at St George's in Great Finborough were broadcast as part of Radio 4's Checkpoint programme in 1982.
He hit boys with objects including a slipper and a wooden bat, leaving many with bruises.
Slade was forced to resign soon afterwards, but was not jailed until 2010 when it emerged that he had also sexually abused pupils.
The 61-year-old, from Burton-on-Trent, Staffordshire, was found guilty of more than 50 sex assaults and beatings, as well as possession of 4,000 indecent images of children.
He was sentenced to 21 years.
But new evidence shows that in the intervening years, Slade used his connections to people such as Derek Sawyer - former leader of Islington Council - to help him get a job as director of education at a school in Africa.
The job was not supposed to involve contact with children, according to Mr Sawyer, who said he was unaware that Slade was a paedophile.
The two men, friends in their school days, set up an organisation called International British Education Projects (IBEP), which won a contract to run four schools in Swaziland.
Slade also successfully bid for £85,000 in funding from a Leicester charity to set up a school for the victims of India's Gujarat earthquake.
While working at a school in Swaziland, he used the pseudonym Edward Marsh - an identity he had falsely acquired using the birth certificate of an eight-year-old boy buried at a Derbyshire cemetery.
The six-month BBC investigation has revealed that pupils in both countries were abused.
The Swaziland school's doctor told the programme he had seen evidence of "excessive corporal punishment and fondling", while children in India said they were beaten and photographed.
Former Labour councillor Mr Sawyer, who has been chairman of the London Courts Board and director of the youth offending charity Catch 22, said he had been led to believe Slade had legally changed his name.
He also said he was kept "in ignorance" about the violent disciplinarian's true nature.
"I was shocked by Derek Slade's conviction for sexual abuse but I am glad that justice has been done for his many victims," he said.
"Like many others, I have been taken in by Mr Slade and used by him. I knew nothing of any allegations of sexual abuse by Mr Slade, nor did I know that he should not have been put in a position of trust with children.
"I have had intermittent contact with Mr Slade over the past 40 years, which I now regret, but if I had known or believed that he was a risk to children I would obviously have had no association with him whatever."
An Abuse of Trust is on BBC One at 22:35 BST on 2 August, and will also be available on iPlayer.