Paramedics performed emergency surgery on Philip Lawrence, 48, after he staggered into a classroom following the attack outside St George's Roman Catholic School, Maida Vale, at about 1500 GMT today.

He was rushed to St Mary's Hospital, Paddington, where surgeons lost their battle to save the father-of-four.

The attack took place when Mr Lawrence went to help a 13-year-old pupil who was being assaulted by a gang outside the 440-pupil mixed comprehensive.

A Scotland Yard spokeswoman said: "It appears that as one of the schoolboys left the school premises he was approached by a small group of male youths. The teacher, who was in the vicinity, intervened.

"The man sustained a stab wound but managed to stagger back into the school and raise the alarm. The suspects are believed to have made off on foot into roads nearby."

Children questioned

The boy was also taken to hospital with head injuries.

More than 20 police officers have converted the main school hall into an interview room to investigate the attack on the head teacher, who had led the school for three years.

Witnesses described seeing Mr Lawrence "staggering and clutching his chest" after the attack.

A spokesman for the board of governors said: "We are shocked and appalled at the sudden and tragic loss of such an outstanding friend and colleague.

"At the moment our thoughts are with his family and we will be offering them all the support we possibly can."

In a television interview last year, Mr Lawrence said he had increased security at St George's to protect pupils, closing some school entrances and installing a video camera at another.

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