People inside Archway Leisure Centre on Macdonald Road were evacuated on Sunday (November 30) after reports of a blaze at 1.37pm.
It resulted in gym-goers, swimmers and those using the sauna facilities having to stand outside – many still in their swimwear.
Pictures show a man wrapped in a towel, while others were given foil blankets to keep themselves warm.
The Metropolitan Police has launched an arson investigation into the incident, although no arrests have been made at this stage.
Enquiries are ongoing, a spokesperson said.
Gary Henson, who was using the gym, said he was at the top of the building when the alarms went off.
He said: “Lifeguards got everybody out within minutes and leisure centre staff had all the swimmers and gym and sauna users out really quick.”
Mr Henson claimed that “nobody could dress or collect their belongings”, which resulted in people wearing their swimwear and gym clothing outside.
Those who were in the pool were provided with the foil blankets and were then asked to go the centre’s assembly area for warmth.
He added: “We were really impressed by how quickly and professionally the centre staff dealt with a complicated situation.”
By the time firefighters arrived, the flame had already been extinguished after the evacuation.
A Met Police spokesperson said: “At 14:09hrs on Sunday, 30 November officers were called by the London Fire Brigade after reports of a fire at Archway Leisure Centre, on Macdonald Road, N19.
“The building was evacuated by the London Fire Brigade. There were no reported injuries and the fire was quickly extinguished.
“Met officers assessed the scene and have subsequently launched an arson investigation.
“No arrests have been made at this stage. Enquiries are ongoing.”
GLL, the biggest leisure centre provider in the country which trades as Better, was approached for comment but this paper has heard no response.
