A care worker has been jailed for six months after he was caught on a secret camera hitting a disabled teenager twice on the back of the head.

The parents of Zak Rowlands, aged 19, noticed he had started flinching when they approached, so decided to place a covert camera in their son's room at the Oxen Barn Residential Home in Leyland, Lancashire.

The surveillance picked up Stanley Nkenka, aged 36, hitting the teenager and then threatening to repeat the assault if he got out of bed.

Mr Rowlands, who cannot speak and is the size of a 12-year-old, was born with a chromosome disorder and has autism and learning difficulties.

Nkenka, from St Ethelbert's Avenue, Deane, pleaded guilty at Preston Crown Court last month to ill-treatment of a person without mental capacity in the early hours of May 12.

The footage showed the defendant bringing Mr Rowlands back to his bedroom after he wandered off during the night and then hitting him.

He then pushed him on to the bed and called him "a stupid boy" .

As the youngster lay in darkness, he later approached him and quietly said: "Do you want some more?" before he went on to strike him again on the back of the head on a separate occasion.

Sentencing him at Preston Crown Court, Judge Christopher Cornwall said: "The ill-treatment that is complained of seems to me to be dismissive of him as an individual, unkind and uncaring, and really disrespectful of him as a human being."

Oxen Barn - privately run by the Priory Group - is a specialist home for adults who have autistic spectrum disorders and severe learning difficulties.

Earlier this year, two care workers working for another Priory Group company in Bury were jailed for seven months after they were caught on a secret camera physically and verbally abusing a quadriplegic man.

Mr Rowlands's mother Julie, from Crewe, Cheshire, told the court: "When I saw the video recording of Nkenka hitting him, I felt sick, heartbroken, angry and incredibly guilty.

"It's hard to articulate the actual words that really describe my emotions. I'm scared, really scared that it will happen again."

The abuse happened on Mr Rowlands's birthday, and they "will always have a blemish attached to them now", she said.

Her husband, Paul, added: " You have damaged the fragile trust that we have in the care of our precious son and that damage can never be fully undone."

In mitigation, Kathryn Johnson, defending Nkenka, said her client had acted in a loss of temper borne out of his frustration with his employers and was remorseful for his actions.

However, the judge noted that the defendant appeared calm and casual on the covert footage.

She said he had felt "undervalued" and "isolated" at work and had complained to his bosses that he was being discriminated against.

Miss Johnson said: "He had been planning to become a nurse. There is no way that will happen now. He has been struggling to find any kind of work."

Appealing to the judge to consider a suspended sentence, she said Nkenka's wife and young child were dependent on him.

His wife was on a student visa and faced having to leave the country if she was not able to return to her studies.

The barrister continued: "He has acted out of character and the events of that night were isolated incidents."

The judge told Nkenka that his complaints about work problems could not "begin to excuse your loss of self-control in relation to this intensely vulnerable young man".