An autistic teenager has won a multi-million pound payout after his parents discovered negligence by NHS staff caused his condition.

For years after Ben Harman's birth, his parents – who live in Marlow - thought his disabilities were just one of life's cruelties and struggled on to make his life as comfortable as possible.

But it was only when they applied for a blue parking badge in 2006 that the truth was "revealed incidentally".

It was finally uncovered that medics at Kent and Canterbury Hospital had negligently failed to diagnose his 'catastrophically low' blood sugar levels after his birth in 2002.

He was eventually given dextrose, but that came too late to save him from devastating brain damage and autism.

A High Court judge ruled: "When he was discharged, his parents were told nothing about the risk that his low blood sugar levels may have caused lasting damage".

Ben’s parents were worried when he failed to meet his milestones, but had no suspicions he may have been a victim of medical negligence.

The judge said that it was in 2006, when the family applied for a blue badge, that the truth came out when the couple were asked for medical evidence to support their application.

Mum Joanne Harman finally sued and the East Kent Hospitals NHS Foundation Trust admitted liability in July 2013.

Following the judge's ruling, Ben, now 13, is in line for massive damages to fund the lifetime of care he will need.

The trust will have to pay his fees at specialist boarding school, Prior's Court in Hermitage, Berkshire, until he is 25.

It will also have to fund his care regime at home.

His parents, originally from Kent, are currently renting a large house, in Marlow so that they can be close to him.

The judge said Ben's thinking skills are seriously impaired and he has the oral communication skills of a six-month-old baby.

His social awareness is only a little higher than that and he struggles to meaningfully relate to others.

"He is prone to having unpredictable tantrums and can lash out physically while shrieking at the top of his voice," the judge added.

"There is a real and continuing risk of injury to himself and to others" and, as he grows older and bigger, his care has become more and more challenging."

His parents had fought tirelessly for funding so he could attend Prior's Court.

By the time he got in to the school, his parents were "at the end of their tether, exhausted by the physical and emotional challenges of looking after him".

The judge said Ben was 'thriving' at the boarding school and comes home for school holidays and every other weekend.

"He has only now started to hug his mother", the judge said, adding that the family had recently taken their first foreign holiday for 10 years.

His parents were determined to welcome him back home when he leaves school at 25, the court heard.

And the judge rejected the Canterbury-based trust's arguments that he would be better off spending his life in institutional care.

The compensation figure has yet to be calculated, but it is believed to be a seven-figure sum.