The murder of a French nanny bears all the hallmarks of a psychosis known as folie a deux, where a delusion is shared from one individual to another, a court heard.

Sabrina Kouider, 35, and Ouissem Medouni, 40, were found guilty of killing Sophie Lionnet, 21, and burning her body in their garden.

Folie a deux, or "madness of two", was apparent in the case, according to the judge, with depressive and borderline personality Kouider the driving force and weak Medouni the willing party.

Kouider collapsed in tears as the jury foreman returned the verdicts, while Medouni hung his head.

Miss Lionnet's mother Catherine Devallonne also wept as Judge Nicholas Hilliard QC said he was sure the allegations made against her daughter by her killers had "no truth whatsoever".

In the weeks leading up to her death in September last year, the couple beat, starved and tortured the shy 21-year-old au pair by dunking her head into water until she confessed to the supposed link to Mark Walton - a founding member of pop group Boyzone and Kouider's ex-boyfriend.

Having killed Miss Lionnet in the bath, the pair threw her on a bonfire in the garden of their home near Wimbledon, south-west London, as they barbecued chicken nearby.