Fire fighters were called to 20 grass fires on Mitcham Common in just three days this week prompting fears of arson.
Crews from Mitcham and Norbury were called out to five fires on Sunday, August 4, on Mitcham Common, and a further eight on Monday.
A further seven fires were recorded yesterday, bringing the total to 20 in just three days.
All of the fires involved grass, shrub or trees being alight and were described as secondary fires which were put out in minutes.
Police have now been informed over suspicion that the fires could have been deliberate as investigations into their cause continue.
A spokesman for Merton police said: "Regarding the fires on the common, the incidents are being investigated by the Fire Brigade investigation team at the moment.
"We have been made aware by them and will take any necessary action following their report."
Last month a fire the size of four football pitches broke out on the Common, destroying four hectares of land.
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