Environmental groups are gearing up for a succession of legal battles over developments after the Western Australian supreme court ruled the environmental approval of a $40bn gas hub was illegal.

WA chief justice Wayne Martin decided that the proposed facility at James Price Point in the Kimberley should not have been approved due to an invalid environmental approval process.

The judgment is a further embarrassing blow to WA premier Colin Barnett, who has enthusiastically backed the onshore development despite Woodside, the lead consortium partner, dropping its plans to build the hub in April. It’s expected that a floating platform will be used to extract gas from the Browse Basin instead.

Chief justice Martin ruled that Christopher Whitaker, Denis Glennon and Rodney Lukatelich, members of the WA Environmental Protection Authority, had suffered a series of conflicts of interest, and should not have participated in the decision-making process. Even though one member, chairman Paul Vogel, who had no conflict of interest, made the final assessment, the court found that the decision was invalid.

He also ruled that the decision by Bill Marmion, then environment minister, to approve the plan despite was invalid because it relied on the EPA’s invalid assessment report.

The judgment stated: “The minister's statement that the Browse LNG Precinct proposal could be implemented subject to conditions was not a valid exercise of the powers conferred upon the minister.”

The Wilderness Society, which brought the case with Goolarabooloo elder Richard Hunter, said that the gas hub, which triggered widespread community protests across the Kimberley, could be the first of many contentious development plans if environmental approvals are handed over to the states.

The Coalition has said it will devolve assessments to states should it win power at the election, with the formation of rapid “one-stop shops” that will shrink federal oversight of large-scale developments.

Barnett said that he accepted the court's decision but that the process could be started again and handled by the state.

“This was a technical legal issue. We are capable of doing some of the world’s best work here; who is going to be better in Canberra to handle environmental issues than us?” he said.

Lyndon Schneiders, campaign director at the Wilderness Society, told Guardian Australia that the environmental movement was gearing up for a series of court cases to “hold the line” against ecologically damaging industrialisation.

“We are looking a big change on how we interact with big developments,” he said. “Previously, we had a degree of faith that the government would look after the public interest, but after the Business Council of Australia started the push against so-called green tape last year, it seems we are looking at more of a litigation culture, like the US.”

“If businesses want to devolve decision making, they should be careful what they wish for. It only creates more investor uncertainty for them. This isn’t a fight we have looked for, but we’re in it for the long haul.”

Schneiders said that the Places You Love group, a coalition of more than 40 environmental organisations, has discussed how to react to what it claims is a watering down of environmental protections.

“We will be looking to the courts to enforce standards – this will be an increasing part of our campaigning,” he said. “We will look at opportunities to go to the courts when state governments look to override the environment and human rights.

“This wasn’t a cheap case but we were overwhelmed by the response from our members. Many of our members don’t really believe in government any more and understand that we may spend less money on other activities if the courts are the ones to protect the environment and nature.”