Detectives from the Violent Crime Taskforce have arrested two people and seized three suspected firearms.
The arrest follows a search of an address in Upminster on Wednesday, 12 December.
Two handguns - one loaded - and a loaded shotgun were recovered.
Two people were arrested in connection with the investigation and taken to an east London police station
A woman, in her early 20s, has been released under investigation.
The other, a man in his mid-60s, has been bailed to a date in early January, while further forensic enquiries are completed.
Also seized in the raid was cash to a value of around £50,000, which is believed to be the proceeds of crime.
Police Sergeant Eddie Cull, of the Violent Crime Taskforce, said: “This arrest shows the determination of the Met to find and seize illegal weapons and arrest those who possess them.
“We want our communities safe and secure and our armed criminals worried. Anyone who has information should contact police and be assured that we will act on your information. If you do not want to give your name you can always contact Crimestoppers on 0800 555 111."