BHP Billiton's Jimblebar iron ore project and Macedon gas development are among 25 projects in Western Australia that were assessed by a compromised environmental regulator, papers tabled in state parliament reveal.

WA Environment Minister Albert Jacob admitted on Wednesday there was a “technical error” in Environmental Protection Agency (EPA) approvals for the projects granted between 2002 to 2012 – namely board members with a conflict of interest.

After the WA Supreme Court decided in August last year to rule the environmental approval process for the Woodside-led Browse gas project unlawful, there was concern about other EPA decisions.

EPA chairman Paul Vogel assessed Browse on his own after four other board members had to stand aside due to conflicts of interest.

Some owned Woodside shares in self-managed superannuation funds, while another was employed by the company’s joint venture partner BP.

The WA government is now introducing retrospective legislation to validate the projects’ environmental approval.

The legislation will not validate the Browse proposal, which is currently being reassessed by an independent panel, Mr Jacob said.

He admitted there was potential for significant market uncertainty until the other assessments were validated.

Mr Jacob said he was incredibly disappointed the mistake had occurred but was working to fix the problem.

And Mr Vogel refused to fall on his sword over the matter, saying no one had intended to corrupt the process.

He said the environment was not at risk and the EPA’s governance procedure had undergone a complete health check to ensure it met legislative requirements.

“In no way do these conflicts (alter) the science of evidence that sits behind every environmental assessment process that we conduct,” Mr Vogel said.

“My judgment at the time was based on Section 13. That was found to be flawed – I accept that.

“I genuinely believed at the time I was managing those conflicts appropriately.”

Opposition leader Mark McGowan said a full inquiry should be held but Labor would support the legislation to validate the approvals.

Mr McGowan said he didn’t accept Labor needed to take responsibility for the problem – despite the fact some of the projects were approved while the party was in office.

He said the environment minister had admitted to causing the “stuff up” after the Liberals changed the rules in 2008 to allow EPA board members with a conflict to make decisions.

Labor legislated to prevent that from happening in 2003, Mr McGowan said.

“The buck stops with the government,” Mr McGowan said.

“It is a mess of their making.”

Greens MP Lynn MacLaren described the mistakes as a travesty.

“How this was allowed to continue for so long brings to question the practices we have in place to monitor processes that ensure state authorities are not corrupt,” she said.