Police had decided against sending a patrol to investigate complaints about teenage girls causing trouble outside a house that was destroyed by a fatal explosion hours later.

Emmad Qureshi, a 26-year-old businessman, died as a blast ripped through a row of three houses in Harrow, north London.

Police are investigating whether the explosion was linked to a purple liquid, smelling like rotten eggs, that was poured into the letterbox of one of the houses that morning.

A 17-year-old girl had phoned police to report that a group of girls, with whom she was reportedly feuding about a boy, were creating trouble outside the house.

The girl, named in reports as Charlotte Anderson, was injured in the blast, as was another 26-year-old man. Both are in a stable condition in hospital.

Today, Scotland Yard said police had taken a 999 call reporting the trouble-makers on Wednesday morning, but had not been told of the purple liquid till after the blast that evening.

While the girl was still on the phone line, she told the police call-taker that the troublemakers were moving away, and she no longer needed police assistance. Accordingly, police did not send a patrol.

That evening at 9.30pm, the row of cottages was ripped apart by an explosion that detectives believe could have been caused by a vapours from methylated spirits or a similar explosive. Recipes for such bombs can be found on the Internet.

Police confirmed they were treating the incident as suspicious, and criminal charges could be brought, but would not say whether they had interviewed the other teenage girls.

A post-mortem examination of Mr Qureshi, completed this morning, found he died as a result of a wound to the neck caused by flying debris.

Police have not yet recovered any of the mystery purple liquid, but expect to gain safe access to the ruins of the three houses in the next day or two.

The girl was pulled from the rubble of 21 Stanley Road by neighbours, and taken to Chelsea and Westminster Hospital.

Detective Chief Inspector Colin Sutton has said her terrace home could have been deliberately targeted.

“There may well be a connection between this liquid and the cause of the explosion that happened,” he said.

“If it were a volatile liquid and in a confined space, it could evaporate into an explosive mixture.”

The other two girls may have gone to the same school as the teenage blast victim: “They are obviously people she knows, who were there to do her some harm,” he said.

“If it is what we think it is, it was targeted - it was not a random person going around blowing up flats in Harrow.”

Andrew Haynes, 44, said it took at least 15 minutes to pull the teenage girl from the wreckage.

He said: “There was a girl’s arm just poking through the rubble and there was a beam on her. It looked like the ceiling had fallen on her and she was entombed in there.

“She was covered in dust, she had lacerations on her stomach and was in a pretty bad way.”

At least 40 people remained in temporary hotel accommodation last night as recovery work continued.

Since Wednesday night, Harrow Council has been providing emergency help to those forced to leave their homes, including short-term funding and transport.

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