The blast in Larkhall happened three days before Christmas 1999

William Gracie was the brother-in-law of Janette Findlay who died with her husband Andrew and children Stacey, 13, and Daryl, 11, in Larkhall.

The haulage contractor was giving evidence at the trial of the gas utility company Transco.

It denies wrongdoing under the Health and Safety at Work Act.

Forty-five-year-old Mr Gracie, who at the time of the incident on 22 December, 1999, lived in Larkhall, now resides in a new house erected on the site of the explosion at Carlisle Road.

Mr Gracie's wife, Senga, was Janette Findlay's sister.

It was as if gas had not ignited William Gracie

He said he woke at about 0530 GMT on the fateful day after hearing a "large explosion".

Mr Gracie said: "I got out of my bed and went to my front door and saw debris lying everywhere.

"Some of it was falling from the sky. I ran back into the house and phoned 999 and told them I thought a gas canister had exploded."

He went to Carlisle Road where he said he saw flames under the living room window of number 40 and at 42 he said the driveway was "shimmering".

"It was as if gas had not ignited," said Mr Gracie.

He told the jury that his sister-in-law was very house-proud and did not allow her husband to smoke in the house, but he added: "He did anyway".

'I just ran in'

Mr Findlay, he said, would smoke roll-ups in the back kitchen.

Mr Gracie's brother Douglas Gracie, who lived in Scotia Crescent, Larkhall, at the time of the incident said he worked as a lorry driver for his brother.

He had left his house at about 0530 GMT on the day of the blast when he heard a loud bang.

Douglas joined his brother and went to where the house had been.

He said they shouted names and looked through the rubble, but there was no answer.

Douglas said: "A policeman approached and said we could not stay there because there was still gas about."

Advocate, Jonathan Lake, for the defence, asked Douglas if he had stopped to size up the situation and see if it was safe to go into the property.

The witness replied: "No, I could see there was a fire. I didn't stop to examine it. I just ran straight in"

The trial continues.