Three former Barnet council workers have been convicted of 28 counts of historic sexual abuse.

Colwyn Baker, David Hennessy and Nigel Putman were all responsible for looking after vulnerable boys as residential care officers at Swaylands School in Penshurst, Kent.

The school was run by the London Borough of Barnet from 1968 to 1994, and the men were today convicted of abuse dating from throughout much of this period.

In a trial at Maidstone Crown Court, Baker, of Craighouse Avenue, Edinburgh, was found guilty of 20 sexual offences.

Hennessy, 74, of Westfields, in Narborough, Norfolk was convicted of six crimes, and Putman, 62, of Kings Road, Slough, was found guilty of two offences.

The jury returned 15 not guilty verdicts, and was unable to decide on a further five charges.

Det Supt Paul Fotheringham of the Kent and Essex Serious Crime Directorate said: “As residential care officers Baker, Hennessy and Putnam were supposed to look after the boys out of class. Instead they exploited the pupils in their care and committed horrible acts over a long period of time.

“The first victims in this case came forward in 2011. But it soon became apparent there had been others affected and officers went to great lengths to ensure no stone was left unturned.”

Police reviewed old school registers and visited potential victims or witnesses in person to ask if they wanted to help with the investigation.

In all, 65 former pupils made allegations, and the three defendants were eventually charged with 48 counts of sexual abuse against 24 children.

Det Supt Fotheringham said some children who tried to resist abuse were beaten or refused food, and their classmates would be denied leisure activities to make the victim unpopular or feel guilty.

He added: “Despite the weight of this corroborative evidence, the three men refused to admit to their crimes. Instead they forced their victims to appear at court and recount the abuse they had suffered all those years ago.”

The men will be sentenced on Wednesday.

Swaylands School, near Tonbridge, was run by the London Borough of Barnet between 1968 until it closed in 1994.

Initially it was for boys with moderate learning difficulties, but from 1987 was redesigned to accommodate boys with emotional behavioural difficulties.

Pupils were placed there from across London and the south east of England.

Hennessy and Baker had previously been convicted of similar offences committed at the school. In 1993, Hennessy was convicted of four indecent assaults and two counts of buggery on one boy. In 1994, Baker was convicted of four indecent assaults and one count of gross indecency, against three boys.

Both men were sentenced to three years for each offence, to run concurrently.

In light of that initial investigation and the fresh allegations, Barnet council commissioned a report from the Lucy Faithful Foundation.

Pete Saunders, founder and spokesman of the National Association for People Abused in Childhood, said: "NAPAC applauds the fantastic work that Det Supt Fotheringham and his team have achieved in bringing these child abusers to justice.

"We are pleased to have worked alongside them in this difficult and sensitive work, and are most encouraged by Kent Police’s caring attitude and behaviour towards the victims of these vile crimes. This case should act as a benchmark for police forces nationally on how to handle this type of investigation."