On Tuesday, 24 August, officers, assisted by the Specialist Firearms Command entered an address on Conley Road, NW10.
A search of the address resulted in officers finding and seizing a Beretta handgun.
A woman, aged 41 years old, was arrested on suspicion of possession of a firearm at the scene.
She was taken into custody at a west London police station and has been released under investigation pending further enquiries.
The Met continues to seize more firearms than ever before amid a continued crackdown on violent crime.
A total of 450 firearms were seized in 2020/2021 compared with 366 recovered in the previous financial year.
The trend is set to continue with 98 firearms seized in the first quarter of this financial year compared with 92 for the same period the previous year.
Detective Inspector Dean Grafton, said: “Officers are working relentlessly to identify and detain violent offenders and seize dangerous weapons from the streets of London and out of our communities.
“The Met continues to deliver on its promise to make London a hostile place for the supply and transport of firearms.”