His twisted behaviour was unmasked late last year when Australian police stumbled across the videos online. The films had been uploaded by someone whose website username contained Moore’s date of birth, Oxford Crown Court heard.

The antipodean authorities traced the site user back to Buckinghamshire-based Moore then tipped off Thames Valley Police.

Oxfordshire detectives interviewed the younger two of the defendant’s victims on November 16, all of whom are now in their teens and cannot be identified for legal reasons. The older two boys did not wish to be interviewed.

The officers then arrested Moore and searched his property on December 1, less than a month after the tip off from Australian police.

They seized a Dell computer, 12 USB sticks, a memory card and a clutch of home CCTV cameras that had been installed in the living room, bathroom and bedrooms of his Princes Risborough home.

Those devices contained thousands of videos and images that Moore had recorded of himself sexually assaulting the four boys, the youngest of whom was just 11 when the abuse started.

In one of the videos, the defendant could be heard calling one boy – then just 12-years-old – a ‘filthy pig’ as he encouraged the youngster to perform a sex act on himself.

Prosecutor Charles Ward-Jackson told Oxford Crown Court on Wednesday afternoon that in one piece of footage a boy was overheard telling Moore to put a video on a popular pornography website. “The defendant says he will,” Mr Ward-Jackson added.

Judge Maria Lamb was told that the boys were encouraged to perform sexual acts on themselves, with each other and on the defendant. They were given beer to drink and in some of the footage appeared drunk. In other clips they were asleep while Moore molested them.

In addition to the pictures that he took himself or distributed online, the defendant had a cache of more than 23,500 indecent images of unknown children – including 513 in the most serious category.

Sending him down for 13 years and four months, Judge Lamb told bearded Moore: “You were an utterly malign influence in their lives. You used each of them for your own sexual gratification.”

She imposed an extended sentence, meaning that the defendant will spend two-thirds of his sentence behind bars until the Parole Board will consider whether he can be released. He must serve an extended three years on licence.

“Had you not been caught when you were I have no doubt you would have continued in your behaviour,” the judge told Moore, who kept his head bowed during the sentencing remarks.

“Unless the risk you represent is addressed, you will continue to be a danger to young boys.”

Moore, of Cannon Place, Princes Risborough, pleaded guilty at an earlier hearing to 33 counts. They included sexual activity with a child, causing or inciting a child to engage in sexual activity, and offences of making, having and distributing indecent images of a child.

Judge Lamb ordered that Moore would spend the rest of his life on the sex offender register. He will be subject to an indefinite sexual harm prevention order limiting his access to young boys.

At the end of the nearly two-hour sentencing hearing, she praised the police for the ‘swift and comprehensive’ investigation that resulted in Moore being brought to justice.