Scotland Yard is to nearly double its resources for fighting gang crime in a renewed crackdown on the problem.
The force has vowed to take a more joined-up approach to tackling gang crime in the capital.
Hundreds of Metropolitan Police officers have conducted a series of raids on properties in a bid to track down and arrest suspected gang members believed to be involved in crimes including assault, robbery and drugs supply.
At a press conference at New Scotland Yard, Assistant Commissioner Mark Rowley said that 109 warrants had been made resulting in 121 arrests for offences including the supply and possession of drugs and gang-related violence.
By midday police said a further 35 warrants had been executed and 37 more arrests made.
Half a kilogram of heroin and a "large amount" of cash were seized from an address in Southwark and a kilogram of heroin, crack cocaine and £10,000 cash was taken in Bexleyheath, with four arrests made there, he said.
The major operation, spearheaded by the Met's newly-formed Trident Gang Crime Command, marks what senior officers have described as a "step change" in the way the force tackles gangs.
Scotland Yard revealed it has now committed 1,000 dedicated officers to fighting the problem, with the creation of the central Trident gang command and 19 new task forces to deal with local gang crime in problem boroughs across London.
There are an estimated 250 active criminal gangs in London, comprising about 4,800 people, mostly aged between 18 and 24, police said.
The force added that gangs, ranging from organised criminal networks involved in Class A drugs supply and firearms to street-based gangs involved in violence and personal robbery, are responsible for approximately 22% of serious violence, 17% of robbery, 50% of shootings and 14% of rape in London.
