A paedophile retired teacher has been given 13 life sentences for 45 sex offences against young boys in England and Thailand.

Mark Frost, 70, who taught at schools in Leyton, admitted to abusing nine children in Thailand between 2009 and 2012.

He pleaded guilty to all of the charges, including six relating to abuse of two pupils at a Worcestershire school during the 1980s and 1990s.

Judge Mark Lucraft called the abuse "horrific and deeply disturbing".

Judge Lucraft handed Frost 13 life sentences, to run concurrently, during the hearing at the Old Bailey.

Frost, previously known as Andrew Tracey, started molesting and raping children while working as an English teacher in the late 1980s.

Despite joining the notorious group PIE - Paedophile Information Exchange - in 1978, which campaigned to legalise child sex, a council allowed him to adopt a young boy in the 1980s.

Frost later moved to Thailand where he raped impoverished youngsters after grooming them with sweets, money, computer games and the use of his swimming pool.

He skipped bail to avoid prosecution in Thailand but was extradited from Spain last year after his activities were uncovered by Dutch police on the computer of a man in the Netherlands.

Frost had got the boys, aged between 10 and 14, to give thumbs-up signs and make heart gestures with their hands while being filmed on a webcam engaging in sexual acts.

After his crimes in Thailand came to light, two former pupils at a Worcestershire school came forward about the abuse they suffered at the hands of Frost between 1989 and 1993.

Frost abused them in a school cupboard, at his home, on a camping trip and elsewhere.

Judge Lucraft said: "This is the most appalling catalogue of sexual abuse.

"It is clear that you have an ongoing obsession with sexually abusing young boys.

"Your conduct to each and every one of these victims is horrific and deeply disturbing.”

In a statement, one of the British victims said: "I have carried this burden for a long time and lived in fear.

"I still won't to this day walk past Mr Tracey's house. I still have nightmares."

Detectives fear there are many more victims yet to come forward, and have set up a hotline in the wake of Frost's convictions.

Senior investigating officer from the NCA's CEOP Command, Matt Sutton said: "Mark Frost is a 70-year-old man who has travelled, lived and worked widely within the UK and overseas, and who was for many years in a position of trust.

"We suspect there could be many more victims, who have never come forward or spoken to anybody about what may have happened to them."

A dedicated NSPCC telephone number for victims has been set up on 0800 328 0904.