Four siblings were left fighting for life after arsonists poured petrol through their Tooting home in the early hours of Sunday morning.

Police said the attack was "not random" and said “local youngsters” would know who was responsible for the attack, which left two brothers and two sisters in a critical condition suffering from burns and smoke inhalation.

Rubina Masud, 53, jumped out of a first floor window with her eldest son, Zain Masud, 22, as fire swept through their Lessingham Avenue home just before 4.30am.

Zain is in a critical condition as are his sisters, aged 21 and 15, and 16-year-old brother Junaid - who were all pulled from the first floor by firefighters wearing breathing apparatus.

Rubina suffered burns but was due to be released from hospital late yesterday.

Neighbours tried to help the family by breaking down the back door but were beaten back by flames.

Detective Chief Inspector Damian Allain, of the Met Police’s homicide and serious crime squad, said the fire was started deliberately.

"Petrol was poured through the letterbox and we have some reliable information and we are acting on it as we speak," he said.

"We have got potential motives, I don't think it is a random attack.”

He added police had several detectives on the case.

He said: "The information we have is that this will have been discussed between local youngsters in the area.

"They will have heard who is responsible for this. They need to look at how horrific this attack was and tell us what they know."

A 15-year-old youth was arrested this morning and is being questioned by police.

Anyone with information should contact police on 020 8721 4805 or call Crimestoppers anonymously on 0800 555 111.

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