Green Party MP Caroline Lucas joined Croydon and Sutton Council candidates and campaigners at a protest against fracking yesterday.
Jean Lambert, London's Green MEP, also attended the rally at Park Hill recreation ground in Croydon to highlight the possible threat posed by hydraulic fracturing, a process of extracting oil or gas from the earth.
In 2008, the Department of Energy and Climate Change granted Northdown Energy Ltd a licence that would allow them to drill for oil or gas in Croydon, Sutton, Bromley and Kent.
It is the only licence of its type granted within the M25.
Ms Lambert said: "Many people aren't aware that fracking is a threat not just to our countryside, but to our capital too.
"It's absurd to even consider drilling for shale gas in our overcrowded city.
"With London's pollution at dangerous levels, instead of taking action to clean up our air, the UK Government and London Mayor just stick their heads in the soil - looking for more pollutants to dig up.
"Fracking is not a quick-fix solution to our energy needs – it's a distraction from the clean green solutions we need.
"It keeps us dependent on fossil-fuels, accelerates climate change, and threatens the local environment with risks to drinking water supplies, air and noise pollution."
Northdown Energy's licence, known as PEDL 245, expires in July. It is thought unlikely that Croydon or Sutton would be suitable terrain for fracking.
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