Slower speeds are expected to hit revenue for the government's NBN.

Slower speeds are expected to hit revenue for the government's NBN. Photo: Peter Braig

The Abbott government expects to make less money from the NBN because of slower speeds available under the Coalition's copper-based network, a Senate committee has heard.

Facing aggressive questioning from former communications minister Stephen Conroy, government officials admitted that the company building the NBN would have to lower its revenue forecasts, partly because of the cheaper, but inferior, technology preferred by the Coalition.

Former communications minister Stephen Conroy.

Former communications minister Stephen Conroy. Photo: Louise Kennerley

There are at least three reasons why the NBN Co expects to make less money from customers on the Coalition's network – which is expected to be about $17 billion cheaper to build than the previous Labor government's NBN.

First, businesses and families will not be able to buy the highest speed plans offered under Labor's NBN, which involved running fibre cabling to 93 per cent of homes around Australia.

The Coalition's alternative NBN, which piggybacks on copper telephone wires for about 70 per cent of households, could not offer “packages” of 250, 500 or 1000 megabits per second, government officials said on Thursday.

Second, it is likely Australians will download and upload less data across the Coalition's slower NBN, which would lower revenue forecasts.

And third, while Labor's NBN was essentially a government-owned monopoly, the Coalition's network will face infrastructure competition from telecoms companies offering other technologies such as HFC (hybrid fibre-coaxial).

Senator Conroy, now the shadow defence minister, was revelling in his new opposition role. He aggressively questioned the government officials whom he oversaw for three years as communications minister.

“Be careful,” was a warning that frequently prefaced Senator Conroy's questions, which were informed by his deep knowledge of the inner workings of the Communications Department.

“All three of you must know the answer to this question … you can't not know this information,” Senator Conroy told the three department secretaries about a question he asked on the products and speeds available under the new NBN.

“Could [the NBN Co] offer a product that it's not possible to deliver in fibre to the node?” Senator Conroy wondered at another point in Thursday's hearings. “Could they offer a product that it's actually not technically feasible to offer?”

Senator Conroy pulled up a PowerPoint presentation to give the department officials a quick lesson on how much data Australians had been using over the past few years.

At another moment in the hearings held at Parliament House, Canberra, Senator Conroy mouthed “don't” to one of the department secretaries, who appeared to be dodging a question about the technical limits of copper wiring.