Officers have arrested four people after recovering a loaded Uzi pistol and around 10kg of cannabis.
Police also seized between £6,000 and £10,000 in cash from a vehicle in Greenford.
At around 6.30pm on Sunday (April 19), armed officers - acting on intelligence - stopped a VW Passat on Ruislip Road, Greenford, near Ravenor Park, and a Ford Galaxy on the M4 junction with Windmill Road.
A man fled from the Passat and was pursued by officers but he escaped.
Officers searched the vehicle and found a loaded Uzi pistol in the rear passenger seat footwell.
They arrested the driver - a 48-year-old woman from Acton - and a 19-year-old man from Ealing, who was in the back of the car, on suspicion of possession of a firearm with intent to endanger lives and possession of cannabis with intent to supply.
The Ford Galaxy was stopped as it was seen leaving a street in convoy with the Passat, before driving off.
Officers arrested the driver - a 44-year-old man from Ealing - and a 20-year-old male passenger, also from Ealing, on suspicion of possession of a firearm with intent to endanger lives and possession of cannabis with intent to supply.
All four are currently in custody at a west London police station.
Detectives subsequently searched three residential addresses: one in Green Lawns, Ealing, from which they recovered ballistic body armour; one in Fletcher Road, Acton; and one in Cedar Grove, Ealing.
