A couple accused of killing their six children in a house fire started the blaze as part of a ''plan that went horribly wrong'', a court has heard Mick and Mairead Philpott allegedly started the fatal fire at their semi-detached home in Victory Road, Derby, on May 11 last year. The family shared an unconventional lifestyle - Philpott, 56, his 31-year-old wife Mairead, and his mistress Lisa Willis, 28, all lived in the same house together. A total of 11 children also lived in the property - six were those of Mick and Mairead Philpott, while four were his children with Ms Willis. Another child was Ms Willis's with a different father. Mick and Mairead Philpott's children - Jade, 10, and her brothers John, nine, Jack, eight, Jesse, six, Jayden, five, and Duwayne, 13 - all died after the fire which engulfed their home as they slept in their beds. The couple, along with a third defendant, 46-year-old Paul Mosley, have all denied six separate counts of manslaughter in relation to the deaths.At the start of their trial at Nottingham Crown Court today, prosecutor Richard Latham QC told the jury of six men and six women that the Philpotts, Ms Willis, and the 11 children had all lived in the house together until February 11 last year. He said the fire, three months later, was no accident and had been started using petrol in the hallway of the house. ''We say that this was a plan that went horribly wrong and resulted in total tragedy,'' Mr Latham said.