SIX guns and ammunition were seized after armed officers from the Met Police searched a van in Essex.
Officers from a specialist north London unit were crossed the border into Essex on an intelligence-led operation on Tuesday morning.
A Met Police spokesman said: "At around 8am on Tuesday, February 25, a white van was pulled over by armed officers on Epping Road in Roydon, near Harlow, in Essex, following an operation by officers from the Specialist Crime North proactive syndicate.
"The driver of the vehicle, a 33-year-old man was arrested on suspicion of possession of firearms, and searched."
Officers then obtained and executed a section 46 firearms warrant on property in Little Brook Road in Roydon.
The spokesman added: "A number of premises on the site were searched, and officers found four handguns and two shotguns.
"All the firearms were loaded and a quantity of ammunition and shotgun cartridges (above and below) were also recovered.
The man remains in custody."
A second man, aged 29, was arrested on suspicion of firearms offences. He has since been released under investigation.
Detective Chief Inspector Driss Hayoukane, who led the operation, said: "Firearms are part of the toolkit of violent criminals, and the Met is committed to taking them off the streets and identifying and arresting people who acquire, use, and seek to make a profit from the sale of firearms.
"Officers are conducting potentially dangerous operations like this every day in order to protect the public, and we will continue in our efforts to bear down on violent crime in the capital."