Openreach's aim to deliver ten million fibre-to-the-premises connections by 2025 could cost up to £6 billion, new estimates suggest.
The infrastructure body is currently consulting with communications providers to identify the level of demand for a major full-fibre deployment.
This estimate of how much the project may cost has been included in a leaked copy of the consultation document seen by the Register.
Openreach is engaging with stakeholders both to gauge demand for full-fibre within the industry and devise new investment, risk and cost-sharing models.
The organisation also wants to reach an agreement on how to migrate customers onto the new platform en masse.
These conclusions could then be used to put together a viable business case for investing in full-fibre.
An Openreach spokesperson said: "Deploying full fibre at scale will cost billions of pounds.
"We are currently in the process of exploring what we can do collectively across industry, government and regulators to minimise those costs.
"The exact costs involved would depend on a variety of factors, which is what the consultation is exploring."
The spokesperson added that the process is ongoing and more details will be shared "in due course".
Clive Selley, Chief Executive of Openreach, is keen to pursue full-fibre broadband as he believes it is "faster, more reliable and simpler to maintain" than copper-based connections.
Furthermore, he argued recently that it could potentially "power the UK’s economic success for a century", but stressed it also "requires a Victorian-scale vision, commitment and investment".