The family of a mother and her six-year-old son, who died more than a decade ago in an unexplained house fire in Bradford, is calling for the case to be re-investigated by murder squad detectives.

Denise Clough, 38, and her son Mark, were killed when a fierce fire swept through their semi-detached home in Broadstone Way, Holme Wood, in April 2003. They were dragged to safety but were both dead on arrival at hospital.

At the time of the fire, detectives investigated whether it was linked to an argument outside the family home two days earlier, and five men were questioned on suspicion of making threats to kill, but no further action was taken.

An inquest into the deaths recorded an open verdict and was unable to pinpoint exactly what caused the blaze.

The inquest was told Mrs Clough's teenage son, Andrew, who staged a burglary at his own home, might have sparked the blaze when he cut a live cable. But investigators could not rule out the possibility the fire was started by a discarded cigarette or was an arson attack.

Now Mrs Clough's younger sister, Diane Ellison, is spearheading a bid by the family to finally get answers to how their loved ones died.

Mrs Ellison, 47, of Drighlington, said it had been a very long 11 years since the fire, and the family had been left with many unanswered questions, some of which may never be answered.

She said the family was initially contacted by family liaison officers and senior detectives, but that ceased quite early in the investigation.

She said: "The officers involved in this investigation backed away from us and left us with no information, no support and no answers. We were treated extremely badly and left feeling like insignificant bystanders.

"I, and my family, would ask that at the very least an unbiased impartial officer looks again at this case and examines all the evidence again fully with an open mind in the hope that maybe we can, after a long 11 years, receive answers and closure for the family, but most of all that Denise and Mark can maybe get the justice they deserved 11 years ago."

Mrs Ellison said the family believed the investigation had been flawed because officers had focused their attentions on Mrs Clough's son, Andrew.

She said: "We accept that at that time Andrew was a complete nightmare to the police generally and created a lot of public nuisance, and this is the reason we believe that the investigation and all evidence was not given the consideration due.

"I do not suggest this was done intentionally, but that the viewpoint of certain officers was simply tarnished."

Mrs Ellison added: "We are not looking to blame anyone. We would just like some closure."

She has contacted West Yorkshire Police and Crime Commissioner Mark Burns-Williamson, and her MP Ed Balls, to ask for their support.

Morley and Outwood MP, Mr Balls said: “Mrs Ellison contacted me to make me aware of the events surrounding the tragic death of her sister and nephew in 2003. I’ve written to the West Yorkshire Acting Chief Constable as well as the Police and Crime Commissioner to ensure the family’s case has been investigated and being dealt with in the proper way.”

Detective Chief Inspector Paul Fountain, who leads West Yorkshire Police's Major Investigation Review Team, said: "A full investigation into the tragic deaths of Denise and Mark was carried out by a Senior Investigating Officer and a team of detectives, and although a number of people were arrested in connection with the incident, there was insufficient evidence at that time to proceed with a prosecution.

"While some cases may be undetected they are never closed, and I would ask anyone with information on those who might be responsible to come forward and speak to our officers by calling 101 or Crimestoppers anonymously on 0800 555 111.

"It is possible that allegiances might have changed in the years which have passed and that those with vital information could now be in a position to tell us everything they know.

"We will also make contact with Diane Ellison to discuss her concerns and establish whether there is any new information that could help us to find those responsible."