A couple in Britain accused of murdering their 21-year-old nanny allegedly forced her to confess to bizarre claims that a former Boyzone member drugged and sexually abused their household.

Jurors were told how Sophie Lionnet was murdered by Sabrina Kouider (35) and her partner Ouissem Medouni (40) for "punishment and revenge", prosecutor Richard Horwell QC said.

Miss Lionnet was allegedly beaten, killed and thrown on a bonfire by her employers after being accused of being "in league" with Kouider's ex-partner Mark Walton, a founding member of the Irish boy band.

Mother-of-two Kouider and Medouni interrogated their nanny for hours to confirm their "perverted suspicions", the court was told.

Jurors heard Kouider had become obsessed with the false idea Miss Lionnet was in league with Mr Walton and in rambling complaints she said he controlled the nanny through "black magic".

Snippets of more than eight hours of mobile phone recordings of the defendants' interrogations were played to the jury.

Jurors were told the aim of the recorded interrogations was to extract some sort of "confession", possibly to later embarrass Mr Walton.

A scientist found she suffered a fractured jawbone hours before her death and she is also known to have suffered bruising, and fractures to her sternum and ribs between 36 hours and three days before dying.

Mr Horwell said by looking at "the state of Sophie" you could tell that the final confession was "anything but voluntary".

Mr Walton has categorically denied the allegations against him.

The Old Bailey in London heard that the couple tortured Miss Lionnet in the bath then threw her body on a bonfire in the garden as they barbecued chicken.

When Miss Lionnet's remains were uncovered by firefighters at the home in Southfields, southwest London, they were initially passed off as the carcass of a sheep.

"Medouni was asked what it was and he replied 'it's a sheep' which he said he had bought from Wimbledon market," the prosecutor said.

He said she was subjected to a "campaign of intimidation, torture and violence" which left her completely "crushed" in the weeks before her death.

Kouider and Medouni, who are both French nationals, deny murder but have admitted perverting the course of justice by burning the body.

Medouni claimed Miss Lionnet died by accident in the bath while he interrogated her, but Kouider said in her defence statement she died in her sleep.

Days before the trial, Medouni served a second defence statement - saying that what he said before was untrue and designed to protect Kouider, and claimed instead that he was woken by Kouider and found Miss Lionnet in the bath.

The trial continues.