Openreach plans to replace the UK’s ageing copper lines with fibre optic cables to bring faster broadband to three million premises by 2020.
Many of BT’s rivals have relied on the Openreach network to supply phone and broadband services to customers.
That prompted regulator Ofcom to order BT to separate from Openreach in 2016 and review its wholesale charges.
TalkTalk has forged a joint venture with Infracapital, the infrastructure investment arm of M&G Prudential, to build a full fibre network for three million premises.
Since creating the joint venture, the planned fibre roll-out has received a boost after CityFibre agreed a £538mln takeover by a consortium of infrastructure investors.
BT’s plans to upgrade the broadband infrastructure will also push up its costs, leading some analysts to revise their earnings guidance.
Earlier this week, Bernstein downgraded its underlying earnings (EBITDA) and revenue forecasts for 2019 and 2020.
It said “investors will have to be patient” as it does not expect a return to earnings growth until 2021.