Police have arrested nine people, including a 14-year-old boy, in a series of raids across London that they say is a “massive blow” to violent gang crime in the capital.

They also seized a Škorpion machine pistol, ammunition, cash and suspected class A drugs in an overnight operation in west London that involved 200 officers.

Some of those arrested were believed to be senior figures in a crack cocaine and heroin-dealing outfit, Scotland Yard said.

An alleged drug-runner, 14, was arrested at his family home. He was among those detained in eight raids in Northolt, Greenford, Fulham and Brentford. Two women in their 30s and a 49-year-old woman were also among those arrested.

The arrests were connected to the established MDP (Murder Dem Pussies) gang, police said, which has been operating in west London for around a decade and has been linked to several murders.

They come as the Metropolitan police faces intense pressure to be seen to be taking action over a spate of violent crimes in London that have left the force with more than 50 open murder investigations.

The nine people were held on suspicion of offences including conspiracy to supply drugs and possession of firearms.

At a house in Dorchester Close, Northolt, young children could be heard crying as dozens of officers flooded inside shouting “police.”

In Fulham, officers noticed a 30-year-old suspect sitting in a car as they crept up to a seemingly empty property in Stephendale Road.

During a search, they found a Škorpion machine pistol, a handgun, 40 rounds of ammunition and a kilogram of suspected class A drugs, Scotland Yard said.

Met officers enter a ground floor flat in Northolt. Photograph: John Stillwell/PA

DI Driss Hayoukane said: “This is a massive blow to an established gang. What we’ve taken out is probably a line which has been supplying the Earl’s Court and Fulham areas.

“This gang have been running that line for quite a while and making a lot of money. These gangs have corrupted children and are using them to ferry drugs. If you look across London, these are the kids that are getting involved in violence and stabbings because they are generally on the streets while the suppliers are removed from it, collecting the cash.”

Members of the gang drove flashy cars and showed off their wealth online with luxury holidays to places such as Dubai, he said.

One property in Earl’s Court had allegedly been “cuckooed”, in which criminals take over the flat of a vulnerable person or addict to sell drugs from it.

2 warrants executed in the early hours by TSG U53 on @MPSHammFul and @MPSKenChel. 1st address revealed 2 guns with ammo, 2kg Crack Cocaine and £50k. Male chased later on and arrested for this. 2nd address - 1 female arrested for supply of Class A Drugs. #ProtectingLondon pic.twitter.com/BIp3NmgRpR — MetTaskforce (@MetTaskforce) April 12, 2018

The operation was the result of about six months of planning by the Met’s Trident anti-gang unit.

The Met commissioner, Cressida Dick, had been on patrol in Hackney, east London, on Wednesday evening, where she said gang tensions were high after a spate of stabbings, including the killing of 18-year-old Israel Ogunsola.

Speaking to reporters shortly before the raids, she said the suspects had been causing devastation and fear in communities.

“They are very violent, several of them have a history of serious violence, at least one is suspected of regularly using a firearm,” she said.

A pair of officers secure a man in a police van after he was arrested during a raid in Northolt. Photograph: John Stillwell/PA

“Not only have they been, as it appears to us, supplying crack cocaine and heroin, they have been making a huge amount of money. They have been exploiting vulnerable people and very young people have been engaged in the drug-dealing operation. So they need to be locked up.

“In the past two weeks or so, and in particular since last weekend, we’ve been doing more and more. The Met is working very hard.”

Sadiq Khan, the mayor of London, said “intelligence-led and targeted” operations would continue over the coming weeks.

“Those committing violent crime, including criminal gangs, will be targeted. Extra resources from City Hall are being used for more enforcement work from our police,” he said.