The 35-year-old's home in Barking, east London, was searched and thousands of child porn images recovered. Some depicted six-month-old babies.

A number of the images fell into the most serious Level 5 category, and showed 'distressed' youngsters struggling against 'sensory deprivation' as they were 'tied up, blindfolded, suspended' and subjected to sado-masochistic acts.

Further inquiries discovered the Pakistani national had also abused a young boy in another country who cannot be identified for legal reasons.

He forwarded pictures of his assaults on the youngster to a fellow paedophile in Britain, London's Southwark Crown Court heard.

Ayaz pleaded guilty to three sex abuse charges related to the the youngster, two of indecently photographing him, and one of distributing the images.

He also admitted two counts of possession - one involving 397 'viewable' indecent pictures of children and the other 112 video clips, all of which had had collected through 'file sharing activities'.

Sentence: His Honour Judge Gregory Stone QC

Sentencing, Judge Gregory Stone QC told the impassive father-of-one: 'One can only conclude that you are driven by powerful paedophile interests.

'Offences such as these cause immense damage to children. Society has utter revulsion for such activity which brings nothing but degradation upon vulnerable children.'

He said some of the images recovered from his computer 'involved children as young as six to 18 months - mere babies - and of the most degrading kind.

'Some of the children are plainly in distress.'

Rejecting a defence assertion that Ayaz's job at Save the Children was simply an 'unfortunate coincidence', the judge continued: 'One very disturbing and worrying aspect of this case is that you sought and obtained work at a well-known children's charity.

'Now I have been assured that, in the circumstances of this case, that has not given you access to vulnerable children.

'Nonetheless, there is concern that you were attracted to this work because it may have appeared to you that it would give you access to such children.'

To his credit was his co-operation with the police, his 'evident remorse', his pleas of guilty and previous good character.

That meant he would not be jailed indefinitely, even though the pre-sentence report made it clear he posed 'a high risk of harm to children'.

But the judge said that, in addition to four years' imprisonment, Ayaz would have to register as a sex offender for life and would never be allowed to work with children. He would also be recommended for deportation.

The imposition of a Sexual Offences Prevention Order would be considered later.

The court heard the qualified book-keeper and accountant came to Britain in January 2008 on a two-year skilled worker's visa.

Peter Zinner, prosecuting, said: 'However, the Crown say he not only brought his special skills as an accountant into this country, he also brought his sexual interest in children.'

Ayaz, who has a 17-month-old child, initially stayed with his sister in Sheffield, but a few weeks later briefly left the country.

When he returned to Britain he moved into rented accommodation in Whiting Avenue, Barking.

Last October he applied for a job as a grants monitoring officer at Save the Children's headquarters in Farringdon, central London, and started the following month.

Despite police fears, it turned out his job did not actually involve access to children or confidential details about them. That meant checks with the Criminal Records Bureau (CRB) at Scotland Yard were not needed.

Mr Zinner told the court: 'Matters came to light by virtue of an investigation into an international paedophile ring, which started off with the arrest of a Norwegian police officer.'

They discovered he had been in touch with Ayaz and provided him with contacts in Romania who could provide at least 15 children for adults to abuse.

He, in turn, passed the information to a fellow pervert in Italy now awaiting trial for child sex offences.

Once Ayaz had been identified, Scotland Yard's Paedophile Unit was informed.

They tracked the defendant down and launched an intensive surveillance exercise.

Save the Children officials were also alerted.

'In view of the potential for contact or at least obtaining the names of particularly vulnerable children, indeed some of the world's most vulnerable children, via his position, police officers acted swiftly and

arrested him at his place of work.'

Since then Oslo police have interviewed the Romanian youngsters, while the Italians have issued a European arrest warrant accusing Ayaz of 'facilitation'.

Mr Zinner said the defendant's computers were examined and more than 2,000 indecent images recovered - mostly of young boys - although many had been deleted.

They included a number of images of him abusing the naked teenage boy.

'The evidence also suggests Ayaz was in regular contact with like-minded individuals, not only in the UK, but also consistent with a paedophile ring involving central and eastern Europe and the Middle and Far East.

'There was also email activity between him and others discussing depraved sexual acts proposed with children for sexual gratification.'

The barrister said although the defendant had no previous convictions, he was clearly a 'predatory and devious international paedophile.

'And perhaps his later audacious obtaining of a job in an organisation which potentially gave him access to contact some of the most vulnerable children in the world, shows he is someone who has a sexual addiction to children and is unable to control it.'

Mr Zinner said the jail sentence of more than a year normally meant automatic deportation.

'However, he is likely to be extradited to Italy in relation to outstanding matters there. So the prospect of him being at large in the UK is very, very limited indeed, and the risk of him committing further offences very low.'

Outside court Detective Sergeant Nick Duffield, of the Met's Paedophile Unit, welcomed the sentence and said it 'sent out a clear message of deterrence to other like-minded individuals'.

Referring to the police investigation, he continued: 'It was important to us that he, being a Pakistani national, didn't get any idea we had become aware of him, and disappear off to Pakistan. For that reason it was vital we arrested him somewhere we definitely knew he was going to be, his place of work.

'Save the Children helped us snare him.'

Ishbel Matheson, a spokeswoman for the charity, said: 'Save the Children has been extremely shocked and horrified by this case.

'We welcome the fact that the judge has imposed  a sentence which will put him in prison. This man clearly represents a danger to children.

'We do think it is important to stress, however, that although he was briefly employed at Save the Children for just over 12 weeks, some of that time he was under police investigation.

'He had no contact with children and absolutely no access to sensitive information about children.

'We fully co-operated with police when they brought this to our attention in January and we hope by co-operating speedily we have contributed in some way to him being brought to justice,' she added.

Read more: http://www.dailymail.co.uk/news/article-1202990/Save-Children-paedophile-jailed-sneaking-Britain-Pakistan-despite-abusing-boy.html