A machine gun and two handguns have been found under a back garden paving slab by police during a raid in South Norwood.
Officers discovered the weapons wrapped in plastic, stashed under the slab surrounded by pot plants and gnomes at a house in Warminster Square at about 11am yesterday.
The firearms found by Trident and Croydon officers were a Mac-10 machine gun and magazine, a Smith and Wesson .44 revolver and a barrel and a cylinder for a Smith and Wesson .44 revolver.
Detective Inspector Phil Holt, of Trident, said: "To the unsuspecting eye, there was nothing about the appearance of this garden that would suggest any criminality.
"Thanks to the fantastic work of our officers we were able to establish that, in fact, beneath the façade of respectability there was something far more sinister being concealed.
"As a result, three more weapons have been taken off our streets and out of the hands of those criminals that might intend to use them."
Three people were arrested in connection with the raid and two of them - Tony Waller, 20, of Towpath Croydon, and Barry Waller, 27, from Stockwell, - have been charged.
They are due to appear today at Camberwell Green Magistrates’ Court via videolink charged with three counts of possession of a firearm with intent to endanger life.
The woman has been bailed pending further enquiries.