The Northolt siege took place in Northolt, West London, England, on 25 and 26 December 1985. It resulted in the shooting of the hostage-taker, Errol Walker. It was the first shooting by an officer from the Metropolitan Police's specialist Firearms Wing. After a domestic dispute, Walker forced entry into his sister-in-law's flat. He took the woman, her daughter, and his own daughter hostage and shortly afterwards fatally stabbed the woman. Negotiations eventually secured the release of Walker's daughter, but he still held the child of his murdered sister-in-law hostage with a large kitchen knife.
Senior police officers were keen to resolve the situation without the use of force and adopted a policy of appeasing Walker, which included withdrawing armed officers from Walker's vision. Almost 30 hours into the siege, Walker ventured onto the communal balcony to pick up an abandoned riot shield. Armed police officers attempted to intercept him but he made it back to the flat before they reached him. The officers threw stun grenades through the windows and climbed through the kitchen window. One officer, Tony Long, found Walker lying on a sofa, holding the knife to the child, and fired three shots, hitting Walker twice.
Walker was knocked unconscious but both he and the girl survived. He was sentenced to life imprisonment for murder, attempted murder, and other offences. Although the Firearms Wing had existed for almost 20 years, Northolt marked the first time one of its officers had opened fire, and the first use of stun grenades by British police. The incident demonstrated the unit's capabilities, which it had been developing for several years. One historian of the unit felt that the incident showed that the police had an alternative for crises that could not be resolved peacefully.