The British oiler, which had been expected to lodge its third - and likely final - environmental plan, has asked for additional time to complete modifications to its submission.

The National Offshore Petroleum Safety and Environmental Management Authority now expects the third iteration of the environmental plan to be lodged by August 31, at which time the assessment will recommence.

Sea Shepherd campaign leader Jeff Hansen has told website Inverse.com that the group, which is better known for taking on Japanese whaling fleets on "scientific" exhibitions in the Southern Ocean, wants to end BP's controversial plans to drill for oil in the Great Australian Bight once and for all.

Initially, it will fight a soft war, using its flagship SSS Steve Irwin on nature tour with "journalists, celebrities, and volunteers" to document the wildlife of the Great Australian Bight and show Australians and the world what would be lost if oil was spilled in the remote part of the world.

The group says drilling, and the risk of a spill in the rough waters along the southern margin, puts about blue whales, sperm whales, humpback whales, minke whales, and the biggest southern right whale nursery in the world at risk.

It used similar tactics in Western Australia's Kimberley region against Woodside Petroleum's plans to develop James Price Point, although that plan was ultimately abandoned by Woodside for fiscal reasons in favour of a floating LNG option for its Browse LNG development, which has also since spluttered.

BP hopes to begin drilling Stromlo-1 this summer, when the seas are less rough.

Sea Shepard says it believes BP will walk away from the Bight if international pressure is brought to bear.

It claims the support of traditional owners in the Bight region.

The tour is set to head out from Williamstown, near Melbourne, on August 5.

The Commonwealth conducted a senate inquiry into drilling in the Bight, however the final report, which was due by June 20, was disrupted by the calling of the July 2 election.

It could be several weeks before counting determines the final make-up of the senate of the forty-fifth parliament and the report is released.