The revised rating, expected next month, will come after a public consultation showed more than 90 percent of locals support the idea that "every effort should be made to preserve [the building] if possible."

Initially, the board in June raised the rating of the building on Government Hill to Grade 2, but even this sparked a public outcry after which four board members resigned.

That grading came after the government declared plans to tear down the West Wing and construct a 32-story commercial tower in its place, saying the historic value of the former office was relatively low.

The board then raised the rating from Grade 3 to Grade 2 and launched a public consultation that ended on August 31.

The June meeting saw the board deadlocked, with members split evenly on Grade 1 and Grade 2 ratings.

Bernard Charnwut Chan then used his vote as the chairman to rate it a Grade 2 building, sparking criticism that he was acting in collusion with the government.

The four members who quit had all voted in favor of a Grade 2 rating.

So it is more than likely that when the next ballot takes place, those in favor of labeling it a Grade 1 building will hold sway.

Should this happen, the government will likely review the redevelopment plan for the West Wing, a source said.

Architecture expert Lee Ho-yin, who quit the board in June, said the West Wing is not of Grade 1 standard but public opinion will have to be taken into consideration since it is a government property.

But Hong Kong Institute of Urban Design president Bernard Lim Wan-fung said the board should take professional opinion into consideration and public opinion as reference only.

Lim said: "The Antiquities Advisory Board is not the Town Planning Board nor a district council, it should not make decisions based on public opinion and should use a more objective standard."

He also believes the board's rating is only one of the considerations and the government should decide separately on whether to redevelop the West Wing building.