Bullied and constantly hungry, the traumatised boy was made to live and sleep in the room, described as a ''cell'' by social workers, and reduced to using a potty as he was locked up each night until morning.

The rubbish-strewn room had no heating, a bare lightbulb, and concrete walls and floor, with the child left to sleep on a dirty mattress with a sleeping bag for a blanket.

The couple in their 40s, who cannot be named for legal reasons, both admitted a single charge of cruelty by wilful neglect between January 2010 and January 2011 at an earlier hearing at Preston Crown Court.

Sentencing, Judge Norman Wright told the pair: "This was a flagrant abuse of power and a gross breach of trust."

He added: "The room has been described as a cell but it seems to me it was akin to a prison cell from a third world country, not the home of an 11- or 12-year-old living in this century in this country."

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The boy was put in the room as punishment for raiding the family's fridge, the couple told police after their arrest.

The room was a windowless old outhouse with one exit bricked up and a new one added leading to the lounge of the family home in Blackpool, Lancashire.

The youngster lived there between the ages of 11 and 12 before his school became concerned as the boy was always hungry in class.

Police and social workers visited the house and he was placed in foster care.

Doctors who examined the boy said he was underweight and below average height for his age, and treated him for anaemia.

Since being placed with foster parents he has put on weight and his behaviour has improved dramatically, described as a "remarkable achievement for him".

But the youngster will have been left traumatised and psychologically damaged by his experience, the court heard at the last hearing.

Lawyers for the defendants said the boy was "undoubtedly" a very difficult child to manage but the parents were inadequate rather than wicked.

Judge Wright said the physical effects to the boy from living in "truly appalling" conditions may have been remedied but the psychological harm "will be unknown".

"It is bound, in my judgment, to be profound," he said.

He said it had been submitted that the child's mother was "subordinate" to her "dominant" partner but he ruled their culpability was equal.

"You were his mother and it seems to me that you were not someone cowered by your co-accused," he said.

"You were in a position to stand up (to him) and you did not.

"Your counsel say that you were someone who loved your son very much. If that was so, how can you behave like this?"

The boy's natural father told ITV Granada Reports: "It was horrible to think that someone had done that to my son. It was horrible. I would never do it to an animal, let alone a child."

He said the child's mother had limited access for him to the boy and he was unaware of his plight.

"I feel guilty," he said. "Guilty because I wasn't there to prevent it.

"Conditions in prison cells are far better than the way my son had been kept and for his age, to be treated like this, it's just despicable."