A former Southampton student described as a prolific and calculating sexual predator has been jailed for 17 years and four months after abusing vulnerable young Kenyan street children.

Charity boss Simon Harris lured boys using food, money and the promise of schooling to his luxury home in the East African country where the abuse took place between 2002 and May 2013.

Harris, 55, was convicted after trial last year of three indecent assaults and five sexual assaults, with one victim thought to be as young as nine.

He was also found guilty of four charges of possessing indecent images of children.

Harris, who sat in the dock at Birmingham Crown Court wearing a suit and tie, never once looked up as the sentences were read out to him by Judge Philip Parker QC.

Addressing the former classics teacher directly, Judge Parker told Harris he was obviously ''intelligent'' and ''charismatic'', which had given him ''a veneer of respectability'', but that he had used this to conceal a ''self-centred arrogance''.

''You designed your life to be close to boys - it suited you to be in education,'' he said.

''It gave you kudos and it also provided a source of boys.''

The judge added: ''It is abundantly clear you have an unlawful sexual interest in young boys.''

Harris, who before trial last year also admitted six counts of indecently assaulting three boys at a college in Devon where he had been a housemaster in the 1980s, had left those victims ''haunted'', and ''revolted''.

Judge Parker said Harris, who later moved to Kenya, had continued his sexual offending against boys, and this time against street children whom he said ''were amongst the most vulnerable in the world''.

''You assumed a hallowed position among the locals,'' said the judge.

''You were revered as someone who could provide the gift of education.

''You were answerable to no-one - and once again you had access to boys.''

The judge added that Harris's charity work in education meant ''no-one batted an eyelid'' when he washed boys, and allowed youngsters to sleep in his bedroom at the remote home he owned on the outskirts of the town of Gilgil.

''You walked on water. But none of them knew you had a sexual motive.''

It emerged during his trial that Harris had been banned from travelling abroad after a 2009 conviction for possession of indecent images of children, for which he served 15 months in a British jail.

However, it was also revealed that he went to court and had the ban, lifted leaving him free to travel back forth to Kenya, where he abused more boys, until he was eventually arrested back in the UK in June 2013 by West Mercia Police.

Judge Parker told Harris: ''You were determined to avoid the English ban and get back to Kenya to live your own life exactly as before.''

He added: ''It had been urged upon me that I should give you credit for all the charitable work you introduced to Kenya, but I am afraid, when your so-called charity work is the vehicle for abuse, I cannot buy into this concept.''

Telling Harrisof, Pudleston near Leominster in Herefordshire,  he was ''a significant risk'' to young boys, the judge said it was clear that his Kenyan victims had been left ''used, degraded, and humiliated''.

''The mental scars will almost certainly never heal,'' added Judge Parker.

Jailing Harris, the judge told the University of Southampton classics graduate he would serve half his sentence on licence and also handed him a life-long sexual offences prevention order.

In bringing Harris to justice, prosecutors used a little-known section of legislation giving English courts jurisdiction to try offences carried out by Britons abroad.

The jury also heard evidence during the eight-week trial from witnesses over a video-link 6,500-miles (10,460km) away.

Detective Chief Inspector Damian Barrett, whose officers led the complex investigation, described Harris as a ''manipulative, predatory sex offender'' and a ''very dangerous'' abuser of children who had ''groomed'' his victims in ruthless fashion.

Colleagues from the National Crime Agency (NCA), whose officers also travelled to Kenya in a bid to trace Harris's victims, described him as ''one of the most prolific child sex offenders'' they had ever encountered.

Kelvin Lay, senior investigation officer from the NCA's Child Exploitation and Online Protection (Ceop) centre, said Harris was ''among the most prolific child sex offenders I have ever come across'', adding ''the precise number of his victims may never be known''.

Welcoming today's sentence, Mr Barrett said: ''The convictions and today's sentence sends an important message to people who have been the victim of crimes such as these to come forward, because time and geography is no barrier to justice.''

He added: ''The emotional impact on the victims of the abhorrent actions of this man is impossible to quantify.

''I hope that the conviction and sentence gives some small comfort to them and our thoughts are very much with them all at this time.''

Harris had faced 23 charges at the start of the trial, but the jurors were unable to agree a verdict on one allegation that Harris had raped a child under 13, and the judge discharged them of their duty in relation to that count.

Judge Parker also directed them to find him not guilty on another count of attempted rape.

All the sex offending happened at Harris's luxury Kenyan residence, known locally as The Greenhouse, near the shanty town of Gilgil, between 2002 and May 2013.

The home, set in acres of lush gardens, was also the base of his charity VAE which placed gap-year teaching students into local schools.

In mitigation, Jeremy Dein QC said Harris ''accepts the essence of these offences''.

But he added that his client's charity work should not be entirely discounted, describing him as ''an exceptional philanthropist.

''He unreservedly accepts the gross misuse of trust and acknowledges the impact of all this on the complainants,'' added Mr Dein.

''He is ashamed of his behaviour - both as a teacher and when in Kenya.''

Throughout, police had believed the charity was used by Harris as a cover story to shield his offending, offering a presentable face to the local community.

In the event, Harris was only brought to justice after a Channel 4 documentary team working on a programme for the Unreported World television series tipped off the police in 2013 about Harris after filming interviews with the victims in Gilgil.

Their information then triggered a joint investigation by the NCA and West Mercia Police into the former teacher's movements in Kenya, in what is understood to be one of the force's most expensive criminal inquiries.

He was arrested at his house in Herefordshire and two computers belonging to him were seized, upon which incriminating pictures of young boys were discovered - including at least one of a Kenyan youngster.