Labor shadow communications minister Michelle Rowland and shadow finance minister Jim Chalmers said in a statement that this estimate was based on an analysis approved by the NBN Co board.

They cited a sensitivity analysis from the NBN Co corporate plan for 2016 which showed these estimates (see below).

The statement said these figures, signed off by the NBN Co board and shareholder ministers, clearly stated that a seven-month delay in the HFC activation profile would have a $1 billion impact on rollout funding.

It pointed out that on 24 May, the Senate had NBN Co confirm the $1 billion figure was based on a seven-month delay, for three million services, with an average revenue per user of $47 per month.

Rowland and Chalmers said it had now been revealed that problems with what they called Malcolm Turnbull’s second-rate NBN could further delay the HFC rollout by six to nine months for up to 2.5 million premises.

Calculating on the basis of the figures signed off by the NBN Board, they said these delays could affect funding by between $420 million and $790 million.

The two Labor officials asked what impact this delay to the HFC rollout would have on funding for the NBN and how much taxpayers' money would be wasted by this latest failure.

“The reality is this – Malcolm Turnbull is deploying a second-rate NBN that costs more and does less. It’s nearly 2018 and he still can’t make it work,” Rowland said. "It's time for Turnbull to come clean about the escalating cost of his unravelling multi-technology mess."