Four fire engines and around 25 firefighters were called to a fire in a garden outbuilding on Sudbury Court Drive in Harrow.
The whole outbuilding was destroyed by fire. There were no reports of any injuries.
The Brigade was called at 2103 and the fire was extinguished by 2344. Crews from Wembley, Northolt and Harrow fire stations attended the scene.
The fire is believed to have been caused by combustible items too close to a heat source.