Australia’s offshore oil regulator is censoring documents about BP’s plans to drill in the Great Australian Bight on the grounds that environmental campaigners could use the information to “oppose all drilling activities” there – and that the plans are too “technical” for the public to understand.

Nathaniel Pelle, a Greenpeace campaign who requested the documents under freedom of information laws, said the decision hindered democratic debate.

Greenpeace sought access to BP’s “well operation management plan”, held by the National Offshore Petroleum Safety and Environmental Management Authority. Nopsema refused access to parts of the document, listing a range of reasons.

It cited one as “the likelihood of opposition/protest groups using the information to oppose all drilling activities in the Great Australian Bight”.

Pelle told Guardian Australia that Greenpeace was appealing the decision. “Obviously civil society groups have a legitimate role in discussing what environmental risks are appropriate,” he said.

In an email to the authority, Pelle wrote: “The implication of this argument is that it is unreasonable for civil society groups to oppose high-risk activities based on the facts. This is not an appropriate determination for NOPSEMA to make.”

Nopsema also considered that some of the document was too technical for it to properly inform the public. “Given its highly technical scope prepared for a confined audience with specific well-engineering expertise, it is unlikely to inform the community about the government’s operations or enhance scrutiny of government decision-making,” it said.

This was despite the FoI Act explicitly stating that government agencies cannot consider whether releasing information “could result in confusion or unnecessary debate”.

“It is unheard of, in my experience, and is clearly not true,” Pelle said. “We’ve had multiple experts from the US and Australia taking part in the debate.”

Nopsema told Guardian Australia it wasn’t appropriate to comment on the matter while it was still possible for Greenpeace to have its decision reviewed.

But a spokeswoman said Nopsema’s chief executive, Stuart Smith, was an advocate for greater transparency, including “for example, releasing full environment plans upfront and providing a public comment period”.

That is not allowed under current regulations, so Nopsema can only release the documents when required to under FoI laws.

Pelle said the level of transparency surrounding offshore oil drilling in Australia was concerning. “We’re the only OECD country that doesn’t require this sort of document to be made public,” he said. “It’s untransparent in a way that is incomparable to other jurisdictions.”

The Department of Industry, Innovation and Science is reviewing Nopsema’s transparency arrangements, considering options that include making environmental plans available to the public.

In October BP – the company responsible for the world’s biggest oil spill in the Gulf of Mexico in 2010 – announced that it was ditching its plans to drill in the bight. But it has continued to pursue its application.

Nopsema told a Senate inquiry in November that the application “was still in play” and BP could sell its right to drill to another company if its application was successful.