Sydney’s most hated building, the brutalist Sirius apartment block at The Rocks, has won the backing of its most powerful ally yet, Sydney’s Lord Mayor Clover Moore.

At a critical point in the battle to have the 1970s concrete building heritage-listed rather than demolished by the NSW Government and the site sold off to developers, she’s thrown her weight behind the conservationists.

“Historic buildings support local economies and communities by contributing to local character, building diversity, urban renewal, design excellence, social cohesion and cultural life,” she wrote in a personal approach to the Minister for Environment and Heritage Mark Speakman.

“These are important qualities for a global city. These qualities strengthen our economy and competitiveness, particularly for tourism and in attracting knowledge professionals.”

Ms Moore’s intervention is a slap in the face for the Government which had been arguing that a heritage listing would cause “undue financial hardship to the owner” – its own NSW Land and Housing Corporation – if it were not able to sell it off for demolition. If it were able to prove that point, it could justify overturning the Heritage Council’s unanimous recommendation that the 79-apartment Sirius be listed.

“But Clover’s support is most welcome and extremely important,” says one of Sirius’s greatest supporters, Millers Point conservation activist Mary Sutton. “She’s said the building does have economic value, can be used for housing and that the socio-economic benefits of heritage conservation to the state should have equal consideration to the property value.

“She’s saying that keeping the building, from an economic perspective, is a net gain.”

Sirius, at 36-50 Cumberland Street, is to some a beautiful, and rare, example of brutalist architecture; to others is an ugly eyesore. It was originally constructed to provide affordable public housing for up to 200 people relocated from The Rocks during the period of the green bans.

Its architect, Tao (Theodore) Gofers, is known to be keen to see the building preserved. Only four to five apartments are still occupied after its Housing Commission tenants were given notice to leave.

A third plan for its future, a complete modern renovation with balconies added on, by architect Chris Bosse, director of LAVA and an adjunct professor at UTS, didn’t win the backing of many, since observers felt it would change the character of the building totally.

But now, with Ms Moore’s added firepower, Sirius’s supporters appear to be closer to winning the heritage listing.

If the Minister’s argument that the building is “incapable of reasonable or economic use” or “causes undue financial hardship” isn’t proven, he may not be able to overrule the NSW Heritage Council’s recommendation and give the go-ahead to Housing Minister Brad Hazzard’s demolition plans.

“And he won’t only have to overrule that, but he’d also have to overcome the fact that the Opera House is World Heritage-Listed, a listing that also applies to all the buildings within the parameters of its view,” says John McInerney, the chairman of the Millers Point action group.

“Then there’s also the planning controls of Sydney Council which protects its current envelope, the opposition of the National Trust who want to keep it and strong community support, as well as the moral obligations of the government. Clover’s now an important ally, and one of a growing band of people who want to preserve Sirius.”

Sirius sits beside the southern approaches to the Sydney Harbour Bridge and looks out towards Circular Quay and the Opera House. It’s currently listed on both the National Trust of Australia (NSW) and Australian Institute of Architects (NSW) heritage registers for its architectural and social significance.

It was named in honour of the First Fleet vessel, HMS Sirius, under the command of Captain Arthur Phillip.