Crews extinguished the blaze by the storeroom at street level of a shop with flats above in New Kings Road.
The fire caused a small amount of damage to a ground water gutter, but no damage was done to the shop.
Investigators believe the fire was caused by the disposal of a cigarette which ignited a build up of debris in a ground water gutter.
A spokesperson says: "We’d rather you didn’t smoke at all, but if you do, it’s absolutely vital you ensure your cigarette is completely out.”