Professor Helen Irving ponders a question that all Melburnians fear in a recent edition of The Sydney Magazine.

"It was always assumed historically that the seat of government and the federal capital would be the same place, even though it doesn't expressly say that in the constitution," Professor says.

"The proviso 'not less than 100 miles from Sydney' was to prevent Sydney becoming the capital by stealth and if the government declared Sydney the capital, the High Court would ask themselves about the history of that provision.

"And every authority supports the seat of government and the capital being in the same place."