A 40-year-old man was taken to hospital and six evacuated from their homes last night following a gas leak.
Firefighters were called to a carbon monoxide alarm in the house in Wandsworth Road at 11.30pm.
A leaking boiler in the property set off the alarm.
The brigade found carbon monoxide in the building and called the gas board.
A 40-year-old man was taken to Whipps Cross Hospital with carbon monoxide poisoning and six people in the road were evacuated.
A spokesperson for the fire service said: "We have had a few lately, but the alarm went off.
"It is a good advert for having a carbon monoxide alarm."