The tragedy was a seminal moment in British race relations, prompting a protest march on central London by up to 20,000 people and acting as a catalyst for the Brixton riots one month later.
Police re-opened the investigation into the blaze 20 months ago, following intense pressure from the families of the youngsters who died.
The official forensic science report, which was passed to police last Thursday, used the latest computer-based techniques and concluded that the fire was started when somebody inside the house set fire to a foam- filled armchair.
George Francis, chairman of the New Cross Parents Committee, said that the families of all the victims now accepted that it was not a racist attack, and were hopeful that the new police investigation would finally uncover the real story.
"It's true most people believe that the fire was caused by the National Front and the police are withholding this evidence, but I don't agree," he said in an interview to be published tomorrow in the New Nation black newspaper. "There was no petrol bomb at all."
An inquest in 1981 recorded an open verdict but the New Cross 13 were widely mourned by the black community and civil rights campaigners as the victims of racially motivated murder. The case has been repeatedly cited during the campaign for justice for the family of black teenager Stephen Lawrence, who was murdered by racists in 1993.
But Detective Chief Inspector Peter Newman, who is leading the New Cross inquiry, said: "The forensic scientist has totally rejected a petrol bomb, explosive or timed device."
He said the new technology had established that only 30 people remained in the three-storey house when the fire broke out at around 5.50am following an all-night birthday party. Sixty people who were at the party after 5.30am are currently being traced and re-interviewed.Reuse content