The Metropolitan Police subjected a severely disabled boy to assault, battery, degrading and inhumane treatment, false imprisonment and unlawful disability discrimination by forcing him into "shackles" at a swimming pool, a landmark ruling has found.

The boy, known as Josh, who suffers from autism, epilepsy and learning disabilities, was forced into handcuffs and leg restraints during a school trip to Acton Swimming Baths in west London in September 2008 after he became fixated with the water and reluctant to leave. The use of restraint was "hasty, ill-informed and damaging" to the boy, who has a mental age of five, according to Sir Robert Nelson, the High Court judge, who found that the restraint was "neither lawful nor justified".

Josh's epilepsy has become significantly worse as a result of his ordeal, and he now suffers from post-traumatic stress disorder. The boy's father, John, told The Independent that Josh was "sobbing inconsolably" after being released by the police and that he "shrinks into himself" every time he sees flashing lights or hears a siren.

The judgment, which awarded Josh £28,500 in compensation, is the first in which police officers have been found guilty of subjecting a member of the public to unlawful disability discrimination, and inhumane and degrading treatment contrary to the Human Rights Act. It is deeply embarrassing for the Met Commissioner, Bernard Hogan- Howe, who has neither apologised to the boy nor accepted that his officers must be better trained to deal with people with autism. In a statement, Josh and his family said the Commissioner was using "public money to defend the indefensible, the shackling of a disabled teenager". His lawyer, Tony Murphy of Bhatt Murphy, said: "This is not an isolated example. The Commissioner must end the widespread practice of using force as a first resort, including when officers are dealing with disabled children."

The police were called by pool staff to remove Josh, against his carer's advice, despite no suggestion of wrongdoing. Officers almost immediately took hold of him, causing the boy to jump into the pool. They then used high-level force to remove him without seeking advice from the carer, and he was restrained. Orders were shouted at Josh, before he was moved to a caged van, soaking wet, on a cold day.

The police failed to consider alternative, safer, more proportionate ways to remove Josh, nor did they make reasonable adjustments for his disabilities, the judge ruled.

His father John said: “When I received the garbled call from the carer I literally thought I'd lost my son, I was in complete pieces. I had to bring the case because my son doesn't speak and I don't want this to happen to anyone else as it could be even nastier. I am very disappointed and disillusioned with the police for deciding to appeal the judgement. An apology [from the Commissioner] would be marvellous, and then I would feel justice has completely been done."