Professor Quiggin said Australia Post was a natural monopoly and ought not to be privatised.

''In general, the price received for assets has been less than their value in continued public ownership. And conversely, in cases where privatisation was proposed but did not go ahead, the actual earnings received have been more than the return from the estimated sale price.''

''The record of privatisation in Australia has been poor,'' John Quiggin, of the University of Queensland, said.

But some economists have warned the government not to sell off the country's remaining Commonwealth-owned businesses, saying Australia had not been well served by the sale of Telstra, Qantas and Sydney Airport.

In the case of Medibank Private - which is likely to be sold - the case was ''less clear cut'' but the issue ought to be assessed as part of general health policy, including proposals to end free bulk billing, he said.

According to the Department of Finance, there are seven federal government business enterprises left: Medibank Private, Australia Post, NBN Co, Defence Housing Australia, Australian Rail Track Corporation, Australian Government Solicitor and ASC Pty Ltd (formerly Australian Submarine Corporation). Other businesses wholly owned by the federal government are AirServices Australia, Australian River Co and the Albury-Wodonga Corporation. The Commonwealth also has a 13 per cent stake in Snowy Hydro Limited.

Last financial year the seven GBEs collected $462 million in dividends for the government, with Australia Post accounting for the vast majority, at $244 million.

Chris Richardson, a director of Deloitte Access Economics, said he was not opposed to privatisation but the government should not sell off businesses in a bid to reduce the budget deficit. '''When government debt and deficits are front-page material, you've got politicians who want to sell stuff. But privatisation doesn't make deficits better … and it's not a panacea for debt.''

Bill Mitchell, of Charles Darwin University, said he was opposed to privatisation because society was typically worse off when it happened. ''The selling off of an enterprise that delivers a cash flow is a ridiculous thing to do.''