The boss of the highly criticised NBN rollout has asked for trust as he vows to have 8 million homes and businesses connected to high speed broadband by 2020.

NBN co-chief executive Bill Morrow said roughly half of the nation’s homes and businesses are now either in the design process, under construction or ready for service.

“This is such a complex undertaking that has never been done before anywhere,” he said. “We know there are strong opinions about much of the details and we accept this.

“We ask that you trust us, we will be transparent, we will be open, we will make sure that we expose all of the elements to which we didn’t do well, on top of the bragging of the good things that the employees did.”

Around 450,000 homes and businesses were added to the NBN footprint in the six months to December 31, taking the number of premises that can order an NBN service to nearly 1.7 million.

The number of homes and businesses with an NBN service rose to 736,000.

NBN charges telcos including Telstra, Optus and TPG to access its fast broadband network, and they re-sell the service to their customers.

NBN Co’s revenue more than doubled to $164 million in first half of 2015/16, from $65 million a year earlier.

Average revenue per user – a key figure for the telecommunications industry – rose 10 per cent to $43 a month over the six month period from $39 a year earlier.

NBN Co was established by the federal Labor government in 2009 to build and operate a superfast fibre broadband network, but after a review of NBN’s plans and costs, the Abbott government decided to use a mix of technologies, including Telstra’s existing copper network.

The bulk of the NBN network will still consist of fibre cables, but the final part of the network that connects to homes and office buildings will use Telstra’s existing copper network.

Some industry experts argue the change will slow broadband speeds.

The design of the NBN will be guided by the government’s policy objectives of providing download data rates of at least 25 megabits per second to all premises, and at least 50 Mbps to 90 per cent of fixed line premises.

Initially, the NBN network was forecast to cost $41 billion, but the cost has ballooned to between $46 billion to $56 billion.

The federal government will cap its investment in NBN at $29.5 billion, with the remainder required to complete the network to be funded by borrowing money.