The cost of the National Broadband Network could blow out by twice as much as the current estimates, according to a new report prepared by the Federal Opposition.

Costs associated with the nation’s largest piece of infrastructure could balloon to $90 million according to the report, and prices for end uses could balloon out to double the rate of household electricity bills.

The Coalition, using industry finance and construction modeling, says the project could take as long as an extra four years and could cost an additional $45 billion to complete.

Coalition Communications spokesman, Malcolm Turnbull, courted the ire of Federal Minister for Telecommunications, Senator Stephen Conroy, who accused the Opposition of establishing a ‘fact free zone’ around the NBN.

“The corporate plan audited by the Auditor-General is produced each year and what we've seen in that corporate plan is $37.4 blllion is the cost of building the NBN, not as today the Coalition are claiming $90 billion,” Senator Conroy told ABC radio.