Four brothers and sisters were critically ill in hospital today after a suspected arson attack on their home.

City banker Zain Masud, 22, leapt from a first-floor window with his mother as their house in Tooting was engulfed in flames. Zain's three siblings were dragged unconscious from the building by firefighters after neighbours and passers-by were beaten back.

Zain's asthmatic sister Nabiha, 21, who is due to be married in October, was resuscitated by paramedics in the front garden and was today critically ill in a specialist intensive care unit.

Zain, his brother Junaid, 16, and sister Maleha, 15, were also described as in a "critical condition" with severe burns and smoke inhalation. Their mother Rubina, 53, suffered burns but was "stable", police said.

It is believed the blaze was started deliberately when flammable material was pushed through the letter box shortly after 4am yesterday. Murder squad detectives are investigating but are yet to establish a motive. Neighbours in Lessingham Avenue said it was a mystery why anybody would want to harm the Masuds, described as "a quiet and respectful family". Today Mrs Masud's close friend Rosemina Ahmad, who visited her at St George's Hospital, said: "She is very upset and worried for her children. She cannot understand why this has happened.

"She told me Zain woke her up and then she tried to get to the others but the fire was too much, so she had to jump. I just thank God they were saved from a greater tragedy.

"I can't think why anybody would hurt them. They are such a good and respectful family. The children have never been any trouble, they mostly stay at home." Mrs Masud's husband Nadir died about two years ago.

Zain had recently been making arrangements for his sister's wedding. It is understood he graduated from City University last summer and works for an investment banking and asset management company in the City.

Family friend Samina Bhatti, 37, whose husband Mumtaz, 43, broke through a back door with a hammer, said: "Zain was crying in the street and Rubina was hysterical. It was awful. My kids are scared to go to sleep because of this. People say it might be a random attack but you don't know if it was racist or someone playing a prank. We could be next."

Law student Cynthia Peterkin, 40, told how she tried to get into the house after driving past and spotting smoke filling the street. She said: "There were bright orange flames inside the house. I sounded my horn to wake people up and then I tried to smash through the windows while my daughter phoned for help. A young man jumped out from upstairs and then an older lady came out. She was screaming, 'Please get my children out'.

"I thought she said there were three young kids inside so I went to the back door and a neighbour helped me smash through. We got inside but the smoke was too much for us. I started to cry because we couldn't get to them.

"Thankfully the fire brigade came and they dragged three people out. At least two were unconscious. They looked badly burned. One was wrapped up in bandages like a mummy. It was really horrible."

Scotland Yard confirmed the fire was being treated as "suspicious" and appealed for witnesses to come forward. A police source said: "Someone has obviously tried to kill them. It is a frightening situation."

• 

  Daughter of Anne Robinson: Mum offered to buy me Botox for my wedding. I was like: 'I'm sorry?'

  Emma Wilson reveals exactly what it's like to be Anne Robinson's daughter — and about stepping out from under her shadow

  ---

• 

  Flame and glory: Rammstein set to light up London

  Sound check: German industrial metal band Rammstein literally play with fire in their live performances - and now they are about to unleash their singeing spectacle on London. Watch out for your eyebrows

  ---