A gang of girls may have used the internet to make a bomb that killed a man and destroyed three homes in their feud with another teenager.

Former classmates of Charlotte Anderson, 17, are being sought by police after a blast destroyed her flat, an apartment above and two neighbouring cottages in Harrow, northwest London.

Miss Anderson suffered serious blast injuries and Emad Qureshi, 26, her neighbour, was killed in the explosion at 9.30pm on Wednesday.

The teenager had called 999 that morning to complain that a group of two or three girls outside were threatening her. She later told police that a liquid the colour of Ribena and smelling of rotten eggs had been poured through her letterbox between 9am and 11am.

Detectives believe that the blast could have been caused by vapours from methylated spirits or from a high explosive such as methyl ethyl ketone peroxide, which can be made from readily available ingredients using instructions found on the internet.

“There are several possibilities, one of which is that this was a home-made bomb,” a police source said. “The methods for making these liquid explosives are all over the internet. They could have gone away and looked them and made them quite easily.

“We have seen with recent terrorism trials that there are plenty of things on the web but it would obviously be a disturbing development if a girl gang has decided to settle a dispute in such a dramatic and tragic way.”

The explosion damaged homes and offices within a 100-metre radius and 40 people were still unable to return to their homes last night as police began to search the rubble. Friends said that Miss Anderson had been involved in arguments with other girls about her boyfriend but police said that this was not part of their investigation.

Detective Chief Inspector Colin Sutton said: “A strong line of inquiry for us at the moment is the dispute, this call at the address and of course the substance put through the letterbox. There may well be a connection between this liquid and the cause of the explosion that happened. If it were a volatile liquid and in a confined space, it could evaporate into an explosive mixture.”

Police believe that Miss Anderson knows the girls who were causing the disturbance and that they may have gone to the same school or college. “They are obviously people she knows, who were there to do her some harm,” Mr Sutton said. “Whoever did this, if it is what we think it is, it was targeted. They may not have intended to cause this amount of damage.”

Miss Anderson has lived alone in the ground-floor flat for some months after leaving local authority care. She was rescued from the rubble by Andrew Haynes, 44, a gravedigger, and two friends after they saw her arm poking through the rubble and heard her screams for help. She is being treated in hospital for severe burns.

Mr Qureshi’s body was removed from the rubble on Thursday night by firefighters. Originally from Pakistan, the businessman had recently finished a postgraduate degree in computing.

A 26-year-old man, a friend of Mr Qureshi, is receiving treatment in hospital after suffering serious head injuries.

Chris Mote, the leader of Harrow council, said that the road might not be reopened for another five or six days.

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