Firefighters were called to a suspected arson attack at midnight in Streatham last night.
Three engines from Tooting and Norbury stations rushed to a block of flats in Gracefield Road.
A fire had been started in one of the corridors outside the door of a young family.
Two parents and their grown-up daughter escaped unhurt after being woken up by their smoke alarm.
The young woman's baby was checked by an ambulance crew but was given a clean bill of health.
Police are now investigating the cause of the fire, which caused only minimal damage to the building.
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