A 77-year-old and a 50-year-old have been arrested after an assault rifle was seized from the boot of a vehicle.
Officers stopped two vehicles in Peckham, south London, at around 5pm on Thursday and found an Armi Jager AP80 .22 rifle with a loaded magazine.
Scotland Yard said it is believed to be a fully automatic assault rifle.
Two men, aged 77 and 50, were arrested on suspicion of possession of a firearm and ammunition with intent to endanger life.
The 50-year-old resisted arrest and a taser was deployed and discharged by armed officers.
He was treated for minor injuries in hospital and has since been released and taken into custody.
The 77-year-old also remains in custody at a local police station.
Detective Chief Inspector James Harper, of the Trident and Area Crime Command, said: "I have no doubt that removing this weapon from circulation has prevented death or serious injury.
"Trident officers will continue to work tirelessly to disrupt and detect such criminality."