An American paedophile teacher who is thought to have abused children around the world for 40 years molested as many as 60 pupils at a school in London.
New Yorker William Vahey, 64, killed himself last month as the FBI began to investigate his offences.
Authorities launched a worldwide appeal to help identify his victims after discovering images of at least 90 children being abused at a school he taught at in Nicaragua on his computer.
Graham Lacey, the head of the Southbank International School in London where Vahey taught between 2009 and 2013, confirmed around 50 to 60 images of pupils at the prestigious school had also been found on his computer, some of which show they had been molested.
The FBI believe Vahey drugged all his victims, meaning many of them may not be aware they were ever abused by the serial paedophile.
Parents now have an anxious wait to see if their child is one of those who were found on Vahey's computer. It is thought Vahey, who taught history and geography at the £25,000 a year school, may have abused the children on overnight school trips.
"This disclosure, which we learned this morning, left us all appalled," said Lacey in a letter to parents. "As a staff we feel upset, angry and betrayed. We can only imagine what you as parents must feel."
Chris Woodhead, the former chief inspector of schools and chairman of governors, described the unfolding crisis as "the worst thing that I've ever been involved in 40 years of education".
There are also concerns about the school's background check after it emerged Vahey was convicted of child molestation in California in 1969.
The school said it had carried out a CRB check on Vahey and examined his employment history for the previous 17 years, which included time spent at schools in Venezuela and Indonesia.
Woodhead said Vahey registered to be a teacher in 1986 and assumed he would not have any prior convictions to be able to do so.
However, according to the Guardian, a regulatory report by the Independent Schools Inspectorate in 2010 said they were concerns about the school's CRB checks. The report said the system was not up to date and "some aspects of staff recruitment have not been completed properly".
Lacey also admitted to the parents at the school that there were rumours regarding Vahey's behaviour following an incident which was investigated by the school, but was not pursued any further by the parents or the child.
"There are perhaps lessons here to be learnt," he added.
Vahey began teaching three years after he was convicted of child molestation at a school in Iran. During his 40-year career, he travelled extensively, talking up positions at schools in countries such as Saudi Arabia, Spain and Lebanon.
After being confronted by employee a the school in Nicaragua about the 90 images on his computer, Vahey said he was abused as a child and admitted to molesting boys throughout his entire life.
His employment was terminated on 12 March and he was found dead in a motel in Minnesota nine days later.
A Met police spokesperosn said: "We are liaising with the school to ensure that any potential victims who come forward to the school or police receive the necessary support.
"At this early stage police believe the alleged victims are boys, who may be aged between 10 to 14 years. However, further investigation is required before we are able to confirm any additional information.
"We are not prepared to speculate on the number of potential victims, there is a large amount of material that must be thoroughly examined."