A gun and a cannabis factory were found after armed police were called following reports of a fight.
Police were called to Hindes Road, Harrow, at 1.45am in the early hours of this morning to reports of a man with a gun in his waistband after a fight.
Officers on their way to the scene were flagged down in Station Road by a 19-year-old who said he had been threatened with a gun by another man.
Firearms officers and the air support unit were called to the scene and the suspect was found in a flat in Hindes Road.
Police entered the flat, where the gun was seized and a cannabis factory was also discovered in one of the rooms.
A 34-year-old man was arrested on suspicion of possession of a firearm and production of cannabis.