A man who was believed to carrying a "pellet gun" was arrested on suspicion of possession of a firearm and imitating a firearm in Northolt.
Metropolitan Police were called to reports of a man seen with a firearm in Rayners Crescent, Northolt, at 9.34am on Tuesday (June 27).
A spokesman for the force said: "Local officers and firearms officers attended the scene and located a man inside a residential address with what is believed to be a pellet gun.
"He was arrested on suspicion of possession of a firearm/imitation firearm with intent to cause fear of violence.
"The firearm will now be subject to forensic examination."
One witness told getwestlondon that they saw armed police at the scene.
Another took a photo of at least seven officers in the residential street, and said the road was blocked.
"[The Police] were trying to get into a property.
“Both sides of the roads were blocked off.
“Lots of armed police.”
The arrested man remains in custody at a west London police station pending further enquires.
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