However, at least one prominent environment advocate and planning expert says the move will result in a net loss of valuable local box gum grassy woodland, and flies in the face of how environmental offsets are supposed to work.

The move follows a closed-session vote in July by Queanbeyan City Councillors to purchase the E2-zoned land from owner Cannchar Pty Ltd. for $450,000. In return, Council would sell it a neighbouring four-hectare block of land also for $450,000, effectively a land swap.

The resolution included a further recommendation that Council grant Cannchar the option to purchase a further two hectares of land north-east of Greenleigh and investigate rezoning it to residential for Cannchar to develop.

A Council spokesperson said around three-four hectares of the incoming Curtis Estate bushland would be cleared as road corridor for the EDE, with the remaining land kept as an offset for the road.

"We are presently in discussion with Office of Environment and Heritage on the suitability of this land to be used to meet some of the offset obligations for the Ellerton Drive Extension," the spokesperson said. "We are reasonably confident that this land will be suitable."

That's despite the fact that the venture- if approved- would result in a net loss of ecologically sensitive box gum woodland to the Queanbeyan environment, given the Curtis Estate land is already zoned for environmental protection.

ANU Senior Lecturer and offset expert, Dr Philip Gibbons of the Fenner School of Environment and Society, said the key principal of environmental offsets to counter loss of habitat caused by development was the principal of 'additionality.'

"An offset should achieve a conservation gain that is additional to what would have occurred anyway," Dr Gibbons said.

"This is a principal espoused internationally, by the federal government and by the NSW government."

And he said any attempt to use environmentally protected land as an offset in a new development was generally prohibited in the federal government's environmental offset policy.

"This is a far cry from best practice," Dr Gibbons said. "The offset assessment methodologies used by federal and state governments in Australia first demand that the proponent exhaust all efforts to avoid and mitigate impacts.

"The final decision is based on the ability to achieve a no-net-loss outcome for the protected matter.

"The application of environmental offset policy in this way will see the area of box gum woodland impacted by the development lost permanently, with no genuine conservation gain to compensate for this loss."

Meanwhile, Council recently referred the 4.6-kilometre link road to the Federal Department of Environment for assessment as a 'controlled action' under the Environment Protection and Biodiversity Conservation Act, due to the ecologically sensitive nature of the land to be developed.