A former St Albans school teacher has been sentenced to three years in prison for possessing thousands of indecent images of children.

David Allison, 48, of Shaw Close, Chertsey, had 500,000 indecent images of children when police searched his home in November last year.

He worked at Sandringham School in Marshalswick during the mid-2000s.

The pictures were on multiple devices and of numerous children taken and recorded around a school where he was working as an assistant head teacher in Surrey. They included photos of girls’ underwear taken without their knowledge.

He was arrested after an investigation by Surrey Police detectives from the Paedophile Online Investigation Team (POLIT).

Detective Inspector Martin Goodwin of POLIT said: “This man blatantly abused his position of trust, giving innocent pupils a false sense of security. He allowed them to believe they were safe from this sort of exploitation and deceived parents and work colleagues alike.

“We have now put a stop to his predatory behaviour and prevented him from continuing with his criminality.”

He had pleaded guilty to three counts of making indecent images of children, one count of taking an indecent image of a child and two counts of voyeurism and was sentenced at Guildford Magistrates Court on January 26.

Det Insp Goodwin added: “The sentencing of this individual sends a message to those abusing a position of trust that you will be caught. Whilst this won’t reverse what he has done, putting this man in prison will ensure his offending does not continue.”

Allison received a lifetime Sexual Harm Prevention Order (SHPO) and is on the Sex Offenders register for life.

Head teacher at Sandringham school, Alan Gray, said: “We are aware of the conviction of a former teacher for offences relating to indecent images. This individual has not worked at our school since 2009.

“We worked closely with Surrey Police and cooperated fully with the investigation, but there was no evidence of any criminal activity during Mr Allison’s time at Sandringham.

“We would like also to reassure parents that our safeguarding procedures are robust and that the welfare of our students is of paramount importance to us.”

Victims of these crimes can seek support from the NSPCC Helpline 0808 800 5000.