He was convicted at Blackfriars Crown Court and has been put on the sex offenders register

A UNICEF spokesman said today: 'We are deeply shocked to hear of the arrest of Peter Newell.'

The 'horrific' sexual assaults took place over a three-year period in the 1960s

But now he is facing six years and eight months in jail for the abuse of a young boy

Newell also helped prepare UNICEF's Implementation Handbook for the Convention on the Rights of the Child

The 77-year-old, from London, led the UK's anti smacking campaign in a long and distinguished career

Peter Newell, a former consultant for UNICEF, was jailed a 13-year-old boy

A leading children's rights campaigner, who helped governments around the world tackle the issue of abuse, has been jailed for raping a 13-year-old boy.

Former UNICEF consultant Peter Newell admitted three counts of indecent assault and two counts of buggery and was sentenced to six years, eight months in prison.

He has also been placed on the sex offenders register indefinitely.

The 'horrific' sexual assaults took place over a three-year period in the 1960s but have only come to light following a police investigation last year.

Newell, 77, of Wood Green, North London, who has led the campaign to ban the smacking of children in Britain, was sentenced at Blackfriars Crown Court on January 3.

News of his imprisonment comes amidst warnings that predatory paedophiles are exploiting the aid sector after 125 British charity workers were accused of sexual abuse in 2017.

The scale of the problem has been laid bare by the scandal facing Oxfam whose staff have been accused of downloading pornography, using prostitutes in Haiti and preying on teenage volunteers in UK shops.

Along with his partner, Rachel Hodgkin, Newell helped prepare UNICEF's Implementation Handbook for the Convention on the Rights of the Child, launched in Geneva in January 1998.

The document, which provides a detailed reference of law, policy and practice aimed at promoting and protecting the rights of children, is still used by governments all over the globe.

It is also used by various United Nations agencies, non-governmental organizations, human rights institutions and academics.

A spokesman for UNICEF said today: 'We are deeply shocked to hear of the arrest of Peter Newell. We had no knowledge of this crime when he worked as a UNICEF consultant over 10 years ago.

'UNICEF has since set in place strong procedures to vet staff and consultants.'

Peter Newell (pictured) carried out the 'horrific' sexual assaults on the boy over a three-year period in the 1960s. He has been placed on the sex offenders register indefinitely

The victim was aged 12 at the beginning of the offences, which took place between May 30 1965 and May 31 1968 at a number of locations in London and the South East.

He reported the abuse to the Metropolitan Police in March 2016 and Newell was interviewed by detectives last May and charged in October.

The balding pensioner was jailed for six years and eight months for the buggery offences and three years and four months for the indecent assaults with the sentences to run concurrently.

Detective Constable Michael Lam-Hang, from the Met Police, said: 'Newell committed a series of horrific sexual offences that have rightly resulted in a lengthy term of imprisonment.

'I would like to thank the victim for his courage in reporting these crimes to police and supporting this investigation. 'I would appeal to anyone who has been a victim of a sexual offence to come forward and speak to police; specially trained officers are there to support you and bring the perpetrators of such crimes to justice.'

Peter Newell admitted three counts of indecent assault and two counts of buggery and was sentenced to six years, eight months in prison

Newell's dark past remained hidden for 50 years, as he fought to end all forms of violence against children, including smacking, not just in Britain but across Europe and the world.

Among his numerous roles, he has chaired the Children's Rights Alliance and was Coordinator of Children are Unbeatable! (CAU!) and the Global Initiative to End All Corporal Punishment of Children.

In the 1990s he was Research Coordinator for the Commission on Children and Violence in the UK.

While spearheading the campaign to outlaw smacking at the CAU! In 2004, Newell reportedly received £80,000 from the NSPCC, Save the Children and Barnardo's which paid for him and three part-time employees.

Approach, a collection of child protection charities and NGO's, which includes CAU! and the Global Initiative to End All Corporal Punishment of Children, say Newell informed the Board of a non-recent allegation of sexual abuse against him in May 2016.

The group said he resigned with immediate effect and that the offences had no connection whatsoever to his former coordinator's role.

Chair of Approach, Denise Stuckenbruck said: 'Whilst we cannot comment on the legal process that has taken place, we condemn all forms of abuse perpetrated against children.

'We have had a new Director in post since September 2017 and our focus is on supporting staff and trustees to continue the important work of the charity to make sure we have maximum impact on children's rights.'

Peter Saunders, founder of the National Association for People Abused in Childhood, who has worked with Newell in the past, said he felt 'betrayed'.

He told MailOnline: 'Last year 94,000 calls were made to our freephone Support Line so NAPAC is totally aware of the impact these crimes have on the victims. No matter how long ago they may have been committed.

'To say I am disappointed to hear of Peter Newell's conviction for buggery and sexual assault would be a massive under-statement. But my first thoughts go to the victim, not to Peter Newell who is now in prison.

'I have to say that knowing now what I know about his crimes I am not surprised at Mr Newell's lack of enthusiasm when I contacted him many years ago to say I was setting up a national charity to support adults who had suffered childhood abuse.

'But what better cover for this man's crimes than to choose to work in the world of child protection. Echoes of some of those creeps who worked for Oxfam and sadly other charities too.

'I certainly hope that he was not employed by any of the charities or NGO's he was associated with for a moment after these crimes came to light.

'The sexual abuse of a child is a life -changing and devastating crime that NAPAC strives to help victims/survivors with on a daily basis.

'I am long past being surprised at these revelations about people of so-called up-standing reputation turning out to have a very sinister side to their character.

'The great thing today is that we are all connecting via the internet. People who thought they had got away with it are being identified and apprehended.

'The police are getting their act together and our friends in the media are shining a spotlight on this dark and thus far secretive world of child abuse.'

Actress Minnie Driver has become the first high profile celebrity ambassador to withdraw her support for Oxfam after the charity's Haiti director Roland Van Hauwermeiren, was one of several staff accused of downloading pornography and using prostitutes, including possibly those under age.

Helen Evans, Oxfam's former global head of safeguarding, later revealed that volunteers as young as 14 were being sexually harassed in some of their 650 shops around Britain while workers on overseas trips had traded aid for sex.

Oxfam was also responsible for 87 complaints of sexual abuse last year according to figures published this week which found that Save The Children and Christian Aid staff were accountable for 31 and two claims respectively.

The British Red Cross admitted to a 'small number of cases of harassment reported in the UK'