The first chief executive of the NBN believes it is inevitable the value of the network will be slashed, saying tough decisions will be needed to rectify the "disastrous" rollout of the project.

Mike Quigley, head of NBN Co under the former Labor government, said the Coalition's shift to a multi-technology model and away from mass rollout of fibre-to-the-premises had hurt the potential of the service and would ultimately cost taxpayers tens of billions of dollars.

Former NBN head Mike Quigley. Credit:Louise Kennerley

Labor has indicated it is open to a write-down of the current $50 billion value, arguing the Coalition’s decisions have reduced the NBN’s value to less than the construction costs and the economics need to be fixed. If elected in May, the opposition also wants to boost access to high-speed fibre connections.

“Do I think a write-down of the NBN assets is inevitable? Yes, I think it is,” Mr Quigley said. “NBN Co and its auditors are likely to come to the conclusion that the [multi-technology mix] just does not have the revenue-generating capability or a long enough useful life to support the valuation currently on the books.”