Met Commissioner Cressida Dick says the drill genre of rap music glamorises violent crime and social media is to blame for a rise in murders in London.
Drill videos that are viewed by millions of people online feature hooded and masked gang members threatening each other with violent lyrics, gestures and hand signals – the term drill is slang for automatic weapons.
The Met compiled a database of more than 1,400 videos to use as an intelligence tool as the force tries to tackle an increase in violent crime.
More than 60 murder investigations have been launched in the capital already this year.
In the past two years, the Met has asked YouTube to take down between 50 and 60 music videos, having to prove they incite violence for the requests to be successful.
The site has removed more than 30 of the clips from the platform – just over half – in cases where they were found to be in violation of its policies.
YouTube, which is owned by Google, said the majority of the videos flagged by the Met were no longer on its platform and the company has developed policies to tackle videos related to knife crime.
Some of the drill music videos still available online feature groups associated with the post code war linked to the murder of Tanesha Melbourne, 17, who was shot dead in Tottenham, north London, last month.
It is not known whether the Met has asked YouTube to remove them.
Detective Superintendent Mike West said the force had been monitoring videos since September 2015.
“The gangs try to out-rival each other with the filming and content – what looks like a music video can actually contain explicit language with gangs threatening each other,” he said.
“There are gestures of violence, with hand signals suggesting they are firing weapons and graphic descriptions of what they would do to each other.
“The Met has got a central database of more than 1,400 indexed videos that we assess and use to gather intelligence.”
DS West said the force only asked for videos which “we believe raise the risk of violence” to be removed.
He added: “Closer partnership work with Google has been developed in the past few months, in order to evolve and increase our capacity to remove social media videos that incite violence, as quickly as possible.”
Ms Dick told LBC radio the videos could be easily accessed on tablets and mobile phones.
“Very quickly, you will see these are associated with lyrics which are about glamourising violence, serious violence – murder, stabbings – they describe the stabbings in great detail, with great joy and excitement,” she said.
“Often, and we’ve seen this in London, we have gangs who make drill videos, and in those videos they taunt each other and say what they are going to do to each other, and specifically what they are going to do to who.”
Pressplay, a company that promotes drill music videos, said on its Instagram page that police had “forced” YouTube to take some clips down because of “what’s happened lately”.
But the same post said the clips “will probably be back up in the next few weeks”.
A group of drill musicians called 1011, whose videos have been removed from YouTube, has launched an online petition, which has so far attracted more than 5,000 signatures.
A YouTube spokesman said: “We work with the Metropolitan Police, the mayor’s office for policing and crime, the Home Office, and community groups to understand this issue and ensure we are able to take action on gang-related content that infringe our community guidelines or break the law.
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“We have a dedicated process for the police to flag videos directly to our teams because we often need specialist context from law enforcement to identify real-life threats.
“Along with others in the UK, we share the deep concern about this issue and do not want our platform used to incite violence.”