A former English teacher has admitted dozens of sex crimes against children in Britain and abroad in one of the worst cases brought to the British courts.

Paedophile Mark Frost, who was previously known as Andrew Tracey, pleaded guilty to a catalogue of abuse against nine children in Thailand between 2009 and 2012.

Since the allegations emerged in Asia, two former pupils of a school in Worcestershire came forward claiming they were sexually assaulted by him in the 1990s.

Frost had sex with one of the boys in a school store room, at playtime breaks at his home where he lived with his adopted son, and at a car park in Woking, London's Old Bailey heard.

Frost admitted charges relating to the historic abuse, as he pleaded guilty to 45 sex crimes at the Old Bailey, although one of the victims died before he was brought to account.

The crimes included multiple rapes, indecent assault, inciting children to engage in sexual activity and making indecent images.

The National Crime Agency believes he may have assaulted many more youngsters he had contact with through his 25-year career in schools and as a senior Scouts volunteer.

The Scout Association said there were "no previous concerns" about Frost, then known as Tracey, until he resigned from the movement after more than three decades upon his first arrest in 1991.

The Association said it had been "co-operating fully with the statutory agencies in this historic investigation".

The NCA has appealed for any more victims to come forward who may have gone to schools in east London, Worcestershire and Hertfordshire where Frost taught under his former name Tracey.

Frost was the focus of a complex international investigation involving the NCA and authorities in Canada, Thailand, the Netherlands and Spain.

Canadian officials had alerted the NCA's child exploitation and online protection centre to Frost as part of its international child porn investigation in July 2012.

But it was not until November 2013 the information was sent on to Thames Valley Police which found he was abroad.

The NCA said it could not rule out the possibility that some of the nine Thai victims were abused in the six months between the time it was first alerted and Frost's arrest in Asia.

The NCA and NSPCC have set up a helpline for more victims to come forward. The number is 0800 3280904.