Smith faces six counts of making and distributing over 120,000 indecent images of children, including 10,000 of the worst category, police said.
According to the Daily Telegraph, Smith moved back to the UK last year and began working at Thomas’s prep school, where he was a deputy head teacher and head of pastoral care in September. He was fired two months later.
His dismissal came after his home in East Dulwich, south east London, was raided by police on Nov 6, where he was arrested.
None of the charges relates to his time at Thomas’s prep and there is no evidence he committed his crimes in the UK at all.
Prior to his role in the UK, Smith was assistant head teacher at the British School in Kathmandu, Nepal, for five years.
He also taught at St Paul’s School, and has degrees from both Oxford and Cambridge.
Helen Dore, senior officer at the National Crime Agency, said: “Child sexual abuse committed online and across borders is a substantial threat to the UK, and it’s one the NCA is committed to tackling.
“We are dedicated to pursuing the most dangerous offenders and to protecting any child who may be at risk, in the UK and across the globe.”