THE cause of a house fire in which a drug addict and her young grandson died remains a mystery, an inquest was told.

A fierce fire broke out in the rented terrace house after Susan Baillie, 40, her boy-friend, Paul Thompson, and her daughter, Joanne, had smoked £80 worth of crack cocaine.

Firefighters rescued five-year-old Jason Baillie, who was brought out of the house with 80 per cent burns and died two days later.

The body of his grandmother was found in the house in Havelock Street, Thornaby, Teesside.

Joanne Baillie, 22, told the Middlesbrough inquest that she was sleeping upstairs and was woken about teatime on November 9 last year by the sound of her son crying.

She said: "I stood up and I was shouting at Jason to come to the door. I opened the door and the flames came up the stairs, so I closed the door.

"I could not see Jason, so I lay back down on the bed because I felt weak.''

She later escaped from the upstairs back bedroom by scrambling on to the roof of an extension.

Drug addict Paul Thompson, of Shepton Close, Thornaby, said in a police statement: "I regularly used crack cocaine on a daily basis and Susan had this same addiction. We would regularly get together and have crack sessions, and Joanne would also get involved."

He said he had fallen asleep on top of a bed he shared with Susan in the front upstairs bedroom.

He got up to let Jason in from school before returning to bed, waking next time to the smell of smoke.

He said: "I could see shards of fire and thick flames coming to the top of the stairs."

He leapt to safety out of the front bedroom window, breaking both his heels, but Susan failed to follow him.

Jason, who was found face-down and partially hidden under a bed upstairs, died at the Royal Victoria Infirmary, in Newcastle.

Fire investigator Peter Dix said the cause of the blaze, which started in the lounge, could not be established with certainty. He said there were three options - that discarded smoking materials caught fire, an electric heater was left near furnishings or, most likely, "a naked flame placed near combustible materials, whether accidental or deliberate".

Police were satisfied no one outside the house was involved in starting the fire.

Coroner Michael Sheffield recorded open verdicts.

He said Susan and Jason died "after three adults had each taken a quantity of cocaine".