Chief planner Andrew Smith said the authority was keen to ensure efficient access to Government House for events such as school visits, ministers being sworn into office, and ambassadors presenting their credentials, as well as when roads were closed as a security envelope was placed around the area for visiting heads of state. There was a question also about how to ensure access to Dunrossil Drive, which leads to Government House, during rush hour in the new suburb – and one option might be a second exit from Government House.

The authority was also looking to protect the ceremonial and symbolic aspects of the approach, he said.

"Practically, that's the beginning of the approach to our nation's head of state," Mr Smith said. "We want to be confident that the approach to Government House is of a quality that's appropriate to nation's head of state ... It's not a standard approach. It's a place where we want to have a high-quality landscape in and around the precinct."

At the moment, Dunrossil Drive leads off Cotter Road directly to Government House, with a grove of oak trees at the beginning and rows of elms and robinias planted in 1918 lining the roadway. It is listed on the Commonwealth heritage list, which says such elm avenues are quite rare, even on a world scale.

The ACT government's plan is to chop off the end of Dunrossil Drive and replace it with a new "Brickworks Road", where four-storey development will be allowed, among 1800 dwellings in the new Yarralumla housing precinct. Dunrossil Drive will meet the new Brickworks road at right angles.

The Australian Institute of Landscape Architects is highly critical of the changes, describing the Dunrossil Drive approach as "one of the great pastoral character landscapes in southern Australia", and saying its ceremonial quality is threatened by the new road plan.

Mr Smith said the end of Dunrossil Drive where it met Cotter Road was "not sacrosanct" but the authority was looking to ensure the quality of the landscape was not compromised.

"The fact that they're relocating [the road] is not the issue; it's what we get after the relocation, and we're just working through all those matters with them at the moment," he said.

Based on the Land Development Agency's sketch plans, the authority was looking for "some improvement … to the landscape structure" and for more detail about access, roads, trees and the overall character of the landscape, he said.

"There's a particular landscape quality in that part of Yarralumla at the moment. and we're trying to understand better what the landscape qualities are going to be at the end of the day," he said.

He welcomed plans for a new road interchange at the Mint as an important piece of infrastructure.

The ACT Heritage Council, though, is not concerned about the Dunrossil Drive changes. Describing it as a "rationalisation" of the roads, council chairman David Flannery said he was "happy with the arrangement", which be believed would strengthen access to Government House and reinforce the Dunrossil Drive alignment.

The council was also pleased to see money to stabilise and protect the Yarralumla brickworks, which he said were in poor repair and unsafe.

The Land Development Agency says the new Brickworks Road would reinforce the role of ceremonial route to the Governor-General's residence, plus become a gateway to the brickworks. A new "Park Avenue" through the new suburb will line up with Dunrossil Drive.

The agency's Dan Stewart said the intent was to "create cohesive, seamless continuation of landscape and vista to Red Hill, and continue formal tree plantings and spacings to match those of Dunrossil Drive". Significant trees would be recognised and integrated into the design, he said.