The National Audit Office (NAO) has expressed concerns that the government and councils will "struggle" to oversee BT in how it completes rural broadband contracts across the UK, after receiving well over £1 billion in public cash.
The government has put in over £500 million of central funding to finance rural broadband projects, and councils have matched that with their own funding.
An NAO report has confirmed the roll-out is two years behind schedule and that the costs presented by BT will have to be closely monitored by government mandarins and council staff, meaning many thousands of invoices having to be scrutinised.
The report said only nine out of 44 rural areas would reach targets for high-speed fibre internet by 2015, and that four areas could even miss a revised 2017 target.
NAO auditor general Amyas Morse said: "The rural broadband project is moving forward late and without the benefit of strong competition to protect public value."
BT has been left to "win" every contract in the programme after other suppliers decided not to enter a framework agreement and Fujitsu pulled out of it, saying they couldn't compete under the terms.
In 2011 the government said 90 percent of premises in every local authority area of the UK should have access to internet speeds above 24 megabits per second by May 2015, and pledged £530m of cash for rural broadband projects to help achieve the target.
As the drive involved state funding it needed EU approval, which took some time to get and which helped to delay the process.
The NAO said that once officials revised projections it was found it would take 22 months longer than first envisaged for 40 areas to reach the goal.
Last week the Treasury revised the take-up target, saying it now wanted 95 percent of UK properties to have access to fibre broadband by the end of 2017.
But the NAO said that past experiences suggested the "government is not strong at taking remedial action to guard against further slippage".
The NAO said it was also concerned that BT says 40 percent of its costs will be on staffing, a figure that "is hard to verify", said the NAO.
The NAO said there had already been one instance when BT was found to be overcharging for management costs to the tune of £3 million.
The NAO said some councils have already said they might not have enough resources to fully check BT's future roll-out charges.
Margaret Hodge MP, chair of the parliamentary Public Accounts Committee, said: "Opaque data and limited benchmarks for comparison means the government has no idea if BT is being reasonable or adding in big mark ups."
A government spokesperson said, "We agree that effective enforcement of the contracts is important and are working with local authorities to ensure this."
A BT spokesperson said: "Deploying fibre broadband is an expensive long-term business and so it was no surprise that other suppliers dropped out as the going got tough."