Four fire engines and around 25 firefighters were called to reports of a garage alight at the rear of a house on Great Cambridge Road in Enfield.
One single storey, timber framed detached garage was destroyed by fire. There were no reports of any injuries.
The Brigade's Fire Investigators believe the fire was caused by the unsafe disposal of burnt materials left beside the garage.
A London Fire Brigade spokesperson said: "If you do have a bonfire, make sure you place it well clear of anything that could catch fire, like garden sheds, garages and fences.
"Damp down burnt materials with plenty of water."
Bonfire safety tips
The Brigade was called at 2208 and the fire was under control by 2248. Fire crews from Enfield and Edmonton fire stations attended the scene.