Police officers swooped on Dover Castle and arrested a deputy head teacher who was conducting a field trip for children.

It followed a raid at the home of Stephen Horn when more than 20 hours of disgusting movies – some including the sadistic abuse of children as young as six – were found.

The 33-year-old teacher was not at his home in Owen Square, Deal, when it was searched in May this year.

He was leading a trip to the castle for children from St Mary's Church of England Primary School, in Ashford, where he was the deputy head.

Horn has now been jailed for 18 months at Canterbury Crown Court.

Prosecutor Dominic Connolly said he was asked if he had downloaded illegal images of children and replied "possibly accidentally".

But he later admitted he had started watching adult porn – but over a 13-year period had then searched for movies and images of children.

He admitted 10 charges of possessing the illegal material at all levels of depravity, which he had saved on two files on his computers.

Smartly-dressed Horn – who sat with his head bowed during the hearing – has since been sacked and will never again be allowed to teach children.

Horn - now of The Street, Womenswold, near Canterbury - blamed a cancer-related illness and the stress at school for his addiction to pornography and admitted he had an interest in child sex images.

But his barrister Lucy Luttman told the judge Horn had never desired to carry out his sexual fantasies on children.

"There has been no suggestion that he has ever behaved inappropriately with a child. He is an intelligent and well educated man who has been plagued with self-loathing and disgust.

"He lived in a fantasy world and is in reality a lonely individual who, because of his medical condition, has never been able to form a meaningful romantic relationship.

"He will now have to live with the shame of what he did and the consequences of what he has done, but he would never have touched children in the way that some of these children (in the movies) were depicted.

"You weren't just a teacher, you were a deputy head and were the person responsible at your school to protect children..." - Judge Simon James

"He has now lost everything that he has spent years building up. He has well and truly learnt his lesson."

Since his arrest, Horn has been working on a relative's caravan and tent park doing horticultural maintenance.

Judge Simon James told him: "You weren't just a teacher, you were a deputy head and were the person responsible at your school to protect children."

The judge ruled it was inappropriate for full details of what the movies and images showed should to be read out in court – and said he did not want to view them.

But Judge James said a police report of the movies and images revealed some of them involved the sadistic abuse of very young children.

He added: "Sadly this prison sentence will complete your fall from grace, but you are lucky to have such support from family and friends who will no doubt help you in the future."

He ordered that Horn remain on the sex offenders' register for 10 years and said he was unlikely ever again be allowed to teach children.

He said parents had every right to look to the courts to ensure children were protected from paedophiles.

The ex-Simon Langton schoolboy had admitted carrying out the offences over a period of 13 years.

He had been formerly employed at Littlebourne Primary School in Canterbury.

In a letter to parents, St Mary's head teacher Kate Harper, assured them police do not believe the images relate to pupils from the Western Avenue primary, or any other school in Ashford.

The head added the offences "did not take place while Horn was at work".

She also stated that all necessary checks had been performed before Horn's appointment as deputy head.