Strike action meant a fire behind shops in Carshalton High Street was able to burn for more than 20 minutes before crews arrived.
The fire, which broke out behind the Village Bakers at about 12.15pm on Saturday, spread to neighbouring shops and caused large amounts of damage although no-one was hurt.
It started during strike action from the Fire Brigade's Union meaning emergency fire contingency crews were the first to arrive on the scene but they took 20 minutes to get there.
Video of the fire taken by Sie Evans
Following the end of the strike at 1pm, 35 firefighters from Purley, Croydon, Wallington, Mitcham and Norbury fire stations came to battle the blaze.
The fire was under control by 2.50pm and the cause is under investigation.