The Greens are using the court ruling that the approval process for the controversial Kimberley gas hub was unlawful, to argue against handing more environmental power to the states and territories.

Yesterday, Western Australia's Chief Justice Wayne Martin found three of the board members of the state's Environmental Protection Authority (EPA) participated in the approval process despite declaring conflicts of interest.

The $40 billion gas hub project, north of Broome, was given the go ahead in the final stage by the EPA's chairman alone.

In the ruling, the environmental approval was found 'unlawful' and invalid.

The Coalition's policy would give states and territories more power to make grant environmental approvals without federal involvement.

The Greens leader Christine Milne says the gas hub ruling shows that should not happen.

"I think everybody should go and read the judgement on James Price Point and just see how Colin Barnett oversaw a process which allowed conflicts of interest with shareholders in Woodside, with people directly involved in this business, to be able to make decisions," she said.

"They were allowed to input to the decision after their conflicts of interest were known."

The spokeswoman for the Broome Community No Gas Campaign, Nik Wevers welcomed the court decision but says the ruling brings other decisions into doubt.

"We were delighted because it justified or validated every concern that we'd raised over the last couple of years," she said.

"We had grave concerns over the EPA decision making.

"We'd certainly be asking, well how many decisions have been made by the EPA where the board members have had a conflict of interest?

"I'm certain that there will be a number of projects that will go back to the drawing board to make some assessment about any approvals or even knock backs that have been made."