The National Offshore Petroleum Safety and Environmental Management Authority has concluded that, after an extended period of deliberation, it was not satisfied that BP's environment plan for exploration drilling along Australia's frontier southern margin had met regulatory requirements.

After a thorough and rigorous assessment BP's environment plan was found not to meet the criteria for acceptance under the environment regulations.

NOPSEMA is now required by law to provide BP with a reasonable opportunity to modify its environment plan.

If BP chooses to resubmit a modified plan, it will then be assessed by NOPSEMA, a process that should take about 30 days from submission.

Stromlo-1 was supposed to be the first of four wells planned for the deepwater Bight, the first wells along the southern margin for almost a decade.

If all goes well, BP plans to drill the well later in the 2016-17 summer, when the treacherous sea state conditions are more benign, but the oiler has so far failed to demonstrate how it would manage the risk of an oil spill and address community concerns about the environmental impact to NOPSEMA's satisfaction.

BP's initial documents warned that a blow-out could take at least 35 days to plug in the best case scenario, with a semi-submersible rig to drill a relief well and emergency capping stacks taking about two weeks to be mobilised to the Stromlo prospect.

Various groups, such as The Wilderness Society, which warned that in a catastrophic event a spill could reach as far as New Zealand, claimed it was proof BP had delivered an inadequate application that had failed to take seriously an oil pollution emergency plan or a comprehensive risk assessment.

TWS said BP should scrap plans for the $1 billion drilling program.

South Australian independent Senator Nick Xenophon said the regulator's decision showed there were "significant and unacceptable risks in the proposal".

"This decision shows that what BP wants to do is hugely complex and risky and needs to have proper oversight and scrutiny," he said.

He said the Great Australian Bight was a priceless Australian asset that should remain undrilled.

Groups opposed to the drilling warned that a spill could devastate South Australia's $422 million fishing industry and coastal tourism across Australia's southern coast, from Albany in Western Australia to Beachpoint on the Victorian border.

A spill could also risk whale nurseries.

SA Greens Senator Robert Simms welcomed the regulator's decision in a statement.

"NOPSEMA's decision to reject BP's risky proposal to drill for oil off the Great Australian Bight is great news for South Australians," Simms said.

"To have a company with BP's shocking environmental record drilling in such an important region would have put both our tourism and fishing industries at risk.

"BP clearly hasn't learned from their disastrous Deepwater Horizon oil spill five years ago.

"The Greens believe that when dealing with complex proposals like this one, the federal environment minister should get the final say and take responsibility for whether deep-water drilling would go ahead or not."

In a statement, BP said it would submit an alternative proposal, although NOPSEMA rules dictate a set number of times it can seek drilling permission.

"Yes, we are going to work hard and take the time to demonstrate we have got our EP [environment plan] right," a BP spokesperson said.

"It is usual for NOPSEMA to provide initial feedback that titleholders need to address before resubmitting an updated version.

"NOPSEMA is a diligent and thorough regulator and we expect to have to work hard and take the time to demonstrate that we have got our environmental plan right."

BP is aiming to use Diamond Offshore Drilling's new $1 billion Ocean Great White rig, which is being completed in the Hyundai Heavy Industries shipyards of South Korea for the operations.

The drilling, if approved, would take place about 250km offshore.

BP is the most advanced of several adjacent exploration projects, ahead of Santos, Murphy Oil, Chevron or Canadian-backed junior Bright Petroleum, which ran into troubles just trying to get permission for its Lighting 3D seismic shoot off King Island.

The last well drilled in the Great Australian Bight was Woodside Petroleum's Gnarlyknots-1A in 2003. The well suffered significant downtime due to bad weather, and while it did not penetrate all objectives, the decision was made to suspend the costly well after the bills kept mounting and no hydrocarbons were encountered.