Opponents of the gas plant say they are now to examine the possibilities of a legal challenge to overturn Government's decision allowing the site.
They claim the application and subsequent public enquiry were held under one set of planning guidelines but the final decision has now been determined under a new set of rules.
Tom Chadwick who is the Chairman of the North York Moors Association said he is "bitterly disappointed" with today's decision, and with plans for another gas plant in a national park and a huge potash mine planned for North Yorkshire, it feels as if the North York Moors National Park is under siege.
A controversial 50 million pound sour gas plant has been given the go ahead on the edge of the North York Moors national park despite huge opposition from locals and campaigners.
Villagers in Thornton-le-Dale near to Malton have fought a three year battle against the plans which will be built on the outskirts of the village.
Opponents say all of the country's national parks will view the approval of the scheme with alarm, because it is claimed this is the first major industrial development to be given the go ahead under new government guidelines.