Environment Minister Tanya Plibersek has told her department to look at whether the legal unit is satisfying an agreement over federal grant money.

Department Secretary David Fredericks says the next payment to the EDO is due on April 30.

He wouldn’t commit to a timeline for the review but said that date was “highly relevant”.

The EDO took Santos to court last year on behalf of a group of Tiwi Islands elders.

They won an injunction that paused work on an underwater pipeline for the $5.7 billion Barossa gas project in the Timor Sea, north of Darwin.

But last month the Federal Court ruled work could resume and Justice Natalie Charlesworth accused EDO lawyers of subtly coaching witnesses, and confecting evidence. Santos has suggested the delays could cost the project in the order of $456 million.

In her judgement, Justice Charlesworth slammed the EDO evidence of Indigenous heritage as “so lacking in integrity that no weight can be placed” on it and said there was “a significant degree of divergence” in the evidence given by Tiwi Islanders.

She said an EDO lawyer and an expert witness had engaged in “a form of subtle coaching” of some Tiwi people, getting them to tell “their stories in a way that propelled their traditions into the sea and into the vicinity of the pipeline”.

During a Senate estimates hearing on Monday, CLP Senator Jacinta Nampijinpa Price asked if the department was investigating the credibility of other cases involving the EDO’s expert, Dr Michael O’Leary.

Fredricks replied: “The department has not done that.”

It was ultimately a matter for the Business Grants Hub as the supervisor of the grants contract with the EDO, he told the committee hearing.

The EDO is budgeted to receive $8.2 million in federal funding over four years.

Federal Opposition Leader Peter Dutton has vowed to defund it, joining the industry group Australian Energy Producers in accusing it of manipulating court systems to stall major projects.

The EDO has called Dutton’s position disappointing.

– AAP