Four police officers suffered stab injuries as they dealt with a man who was causing a disturbance in Kingsbury, Harrow, on Saturday.
When they were alerted to the violent man, the officers attempted to speak to him. However, the man ran into a local butcher's shop and grabbed a knife. He stabbed the officers when they tried to overpower him.
One of the officers was stabbed in the stomach, another sustained head injuries and a stab wound to the arm, the third officer was stabbed in the leg and the fourth officer sustained a broken hand and a broken thumb. All of them were taken to hospital.
"These officers put their lives on the line by confronting this man in what was an extremely violent and spontaneous situation. The four officers have demonstrated outstanding bravery and this once again highlights the dangerous situations our officers deal with on a daily basis as they carry out their duties keeping Londoners safe," Commander Christine Jones of Territorial Policing said in a statement.
"This was an appalling attack on brave individuals who work tirelessly to protect our communities and keep our streets safe," London Mayor Boris Jonhson was quoted by the BBC as saying.
Metropolitan Police Commissioner Bernard Hogan-Howe said: "It was shocking that on a hopefully quiet Saturday morning in a London residential area we had such a terrible incident. It just shows the difficult job that police officers do."
A 32-year-old man was arrested on suspicion of attempted murder.