Mr Turnbull's attack came as Telstra's rivals warned minor party senators that delaying legislation designed to force the break-up of Telstra could leave them powerless to add amendments guaranteeing regional services and consumer protection.

Speaking to businessday, Mr Turnbull intensified the Opposition's criticism of the $43 billion national broadband network, arguing that there was little evidence of sufficient consumer demand. The Government says that by offering speeds of up to 100 megabits per second for 90 per cent of homes and businesses it will spur development of applications and business opportunities.

"History is littered with cases of the 'build it and they will come' mindset, such as Sydney's cross-city tunnel and the rush to lay deep-sea cables in 1990s, which saw huge losses by their private sector backers," Mr Turnbull said. "In this case it would be Australian taxpayers taking the risk and wearing the loss."

The cross-city tunnel fell into receivership in 2006, less than 18 months after it opened, with traffic still less than half the initial forecast, while sub-sea telecommunications cables - including one owned by Reach, a company that had Mr Turnbull on its board - pushed several companies into bankruptcy due to lack of consumer demand.

Meanwhile, the Competitive Carriers Coalition, which represents Telstra's smaller competitors, yesterday warned that the proposed legislation could be rendered obsolete if it was shelved until next year.