Official opening: The Opera House was completed in 1973. Credit:Geoff Bull

The report drew on a survey of 2500 Australians and more than 600 people from Britain, the US, New Zealand and China. The foreigners regarded the Opera House brand as more ''relevant and esteemed'' than that of Australia itself. Show them a picture of the Opera House and they will say Australia more readily than they will if shown a map of the nation, Ms Herron says. Under her stewardship, the house is preparing to embark on a 10-year renovation or ''renewal'' program that, on previous estimates, could cost $1 billion.

When she and the Deloitte partners conducted a media briefing on Wednesday, she was asked if the report was an elaborate memo to Joe Hockey and Mike Baird, the federal and state treasurers, whose budgets will carry most of the burden of any capital works.

''I wouldn't say so,'' she said. Firstly, she rejected the validity of the $1 billion figure, saying the cost would not be known until the House had completed its master plan, now under way with $13.7 million from the state government.

But Herron said putting a monetary value on the house was ''one of the things to do because in this massive, ambitious renewal project we're looking at, basically, we have to hit every note. So we have to look at the people in treasury, both in the state and federal governments, who are going to look and say, 'Why would we do this?' And we provide them with some background information that shows them the value of the Opera House, not based on gut feel but on this extensive research.''