A school IT assistant who forced girls as young as 11 to perform sex acts over the internet has been jailed.

Martin Herzog, 25, of Carshalton, called himself "Sandra" on internet chat rooms and said he was only 15 as he pressurised the girls to perform sex acts in front of him on a webcam.

When police raided his home in Arlington Drive, he was found to have over 4,500 of sickening images of child pornography on his computer, including more than 100 of the most graphic kind, that can include images featuring sadism or bestiality.

The dad-of-one, who was employed at The John Fisher School in Purley, when he was arrested on September 16, 2010, was jailed at Southwark Crown Court on Friday.

He had previously pleaded guilty to inciting underage girls, one of them under 13, to engage in sexual activity between January 2009 and September 2010, pleaded guilty to five counts of making indecent images of a child and five of possessing indecent images with a view to distributing them.

In interview he had said he had been in the chat room to ‘protect the girls from men who might abuse them.’ Lesley Jones, prosecuting said that police found the images on his computer - more than 2,000 of which he planned to distribute to others through a file-sharing network.

Matthew Chidley, defending said: "This amounts to cyber sex, and never once made any attempt to meet with them or engage in any physical activity."

Sentencing him Judge John Price said: "When speaking to this 11 year-old, he, the defendant pressures her into sexual activity.

"But this is not in person, this is in the cyber sex form. He did not meet the girls but he did get them to do things and he watched them.

"I believe that you did this for your own satisfaction, and I reject the idea that you were doing this to protect the girls.

"It was for your own sexual gratification."

Judge Price said the pictures were "totally and utterly repugnant images of real children being abused."

John Fisher headteacher Mark Scully, said: "Martin Herzog was employed as an ICT assistant technician until his arrest in September 2010 and had minimal contact with pupils in his day to day duties.

"The Metropolitan Police have confirmed that his conviction is in no way related to his employment at the school and that our robust ICT systems are completely safe and secure. He has been dismissed as a result of his conviction."

"All victims of child abuse remain in our thoughts and prayers."