BT will be an integral part of keeping Londoners safe after the Met Police picked the telecoms giant to provide a wide range of networking and IT services.
The FTSE 100 firm will provide high-speed fixed and wireless networks alongside cloud and emergency service support.
As part of its services, BT will also support the world's largest roll-out of body worn video cameras, with 22,000 devices set to go online.
The police force said it used EU best practice in the tendering process and will pay BT around £100m for the services.
Colm O’Neill, the managing director of BT business and public Sector said: “We’ve built a longstanding relationship with the Metropolitan Police and are working with them to help them find better, smarter and more productive ways of working."
The Met's back-office IT support systems will be revamped as part of the contract, in an attempt to provide a slicker rostering process for the capital's bobbies.
And cloud-based technology will help the Met cut costs through more flexible used of IT. BT pledged to deliver a "robust and reliable network capable of transmitting voice and data with the appropriate levels of security".
O’Neil added: "Our systems will greatly enhance the way the force organises itself and responds to crimes across the capital, while reducing its IT and infrastructure costs.
Moving to a cloud-based infrastructure, for example, will allow the Met to get even more services for less money, helping it to invest in future policing priorities.
The Met Police force is in the middle of transforming the way it works and the contract will help it achieve its goal of being the "safest global city", BT said.