Just days after a scathing report into the project, it can be revealed the project has also been plagued by the exit of senior managers charged with overseeing construction, and hold ups to the completion of final designs.

More than 13 months after construction began, sections of the line along the busy arterial route of George Street remain far from finished – even though deadlines for the work were extended in September.

Work on George Street has been dogged by the discovery of utility cables under the roadway, holding up construction of the line and leaving little sign of progress for shopkeepers and pedestrians.

There remains little chance that the first sections of track along George Street will meet their new dates for completion of January or February.

Two stretches in Randwick and Kensington have already missed their new deadlines of last month, while several other sections in the city's south-east risk failing to meet targets for completion this month.

And despite work starting more than a year ago, the final designs by the contractor for construction of the line are yet to be finished.

The project director overseeing construction, Mike Millar, has left for another role at Spanish company Acciona, while construction manager Mac Harvey decided several weeks ago to "take an extended sabbatical to spend more time with his family".

Acciona – the partner building the line as part of the ALTRAC consortium – and the government have been locked in backroom squabbles for months over claims by the contractor for costs incurred from modifications to the light rail line.

"There has been a lot of back and forth, and game playing," a source said.

However, the government has rejected speculation that the claims by the contractor will lead to further blowouts in the $2.1 billion cost of the 12-kilometre light rail line.

The contract allows Acciona to make claims for costs incurred from modifications to the original design, such as changes to the location of the light rail stop at Randwick Racecourse and the alignment of the track on Alison Road.

In a thinly-veiled warning to the builders, Transport Minister Andrew Constance said he expected any contactor delivering a project for the government to meet their obligations to the people of NSW.

"I have made that expectation perfectly clear to ALTRAC," he said on Sunday.

The first trams are scheduled to start running on the new line in early 2019, the year of the next state election.

Last week the state's Auditor-General released a damning report into the light rail line, in which it was revealed the government misled the public about the reasons for the $549 million blowout in the cost of the project in 2014.

Sources say that blaming the latest delays in construction on George Street on the discovery of utilities underground is a weak excuse.

"The simple fact is that they have inexperienced people doing this. They have overlooked the complexity of the job," one said.

The risk of further construction delays comes as Sydney lord mayor Clover Moore renewed her threat for the City of Sydney Council to refuse to hand over its next payment of $47 million to the government for the project because it believed it was not living up to what had been promised.

"The state government's light rail design is inadequate and the NSW Auditor-General's report puts a spotlight on what's caused the serious problems," she said.

"There are fundamental breaches of the City's agreement with Transport for NSW."

The council has handed over only $68 million of the $220 million it has committed to the light rail project.

A spokesman for ALTRAC said the consortium had always maintained that dates for completion of sections of the light rail line would change during the course of the project "and that's already been the case".

"Every construction zone has contingency built into the program. This is a normal part of a major construction project of this nature," he said.

"As with all major projects, the CBD and South-East Light Rail design has been refined on an ongoing basis before construction."

The consortium was working to complete the light rail line as per the contract, and the project remained on schedule for tram services to begin in early 2019, he said.