The headquarters of the Metropolitan Police have been sold to Abu Dhabi developers for £370m.
New Scotland Yard has been sold to Abu Dhabi Financial Group for £120m more than the guide price.
The building on Victoria Street, in Westminster, has been the headquarters of the Met Police since 1967.
London Mayor Boris Johnson said: “This landmark deal allows us to preserve the past whilst giving today's Met a vital cash boost.”
Asked if he feared there would be criticism that another investor from overseas has moved into the capital, Mr Johnson said there was no economic difference between “having an investor from Abu Dhabi or having the BP pension fund do this”.
“Anybody who thinks otherwise is, I'm afraid, completely economically illiterate,” he added.
The property was put on the market by the Mayor's Office for Policing and Crime (MOPAC) in September, for a guide price of £250m.
The site will become residential but will probably also feature offices and a hotel, according to mayor.
He said while New Scotland Yard would be redeveloped, the “special triangle jobby” – the revolving sign outside – would be kept.
Abu Dhabi Financial Group said it planned to create a “world-class development”.
The Met is moving to a new headquarters in the Curtis Green building on Victoria Embankment.
The force has raised £215m through the sale of 52 buildings in recent years.
Proceeds from the sale of the 1960s block will be partly spent on new technology to supply officers with tablets, smartphones and body cameras, enabling them to spend more time out on the streets, the Mayor of London's office said.
When completed in 2016, the restructure will save London's police force more than £60m in annual running costs – enough to fund 1,000 officers, the mayor's office added.
But Green Party London Assembly member Jenny Jones said: “The mayor has promised more frontline policing but he has failed to deliver this.”
Met Commissioner Sir Bernard Hogan-Howe said: “We now expect to need to be making savings of up to £1.4bn by the end of the next spending review, including some £600m which we will have delivered by 2015-16.
“This is equivalent to a third of the Met's original budget so this money is absolutely vital to us.”