Ofcom has told Openreach that its ability to strike a deal over fibre co-investment with a rival firm will be a "key test" of its new regulatory approach to BT.
Earlier this year, BT agreed to the watchdog's demand for its infrastructure subsidiary to become a distinct and legally separate company.
As part of this agreement, Openreach is required to offer its own distinctive branding, with any traces of BT's imagery removed to reflect its greater independence.
The deal with Ofcom also means that Openreach is being run by a newly-established board, the majority of which consists of directors independent of BT.
Since reaching this agreement, Openreach has begun seeking views from telecoms operators about the commercial appetite for fibre broadband.
A consultation has been launched to gauge opinion from the likes of Sky, TalkTalk and Vodafone on deploying fibre technology more extensively.
Ofcom is keeping a close eye on Openreach's actions as it seeks to establish itself as a more independent entity.
As a result, it believes the infrastructure body's ability to strike a "co-investment deal with another operator" following the consultation will be a major indicator of whether its regulatory approach is working.
Speaking to an inquiry by the Digital, Culture, Media and Sport Committee, Ofcom Chief Executive Sharon White said: "I would also say a key test over the next few months is: does Openreach manage to do a co-investment deal with another operator for some of these very fast services?
"I think that will be a key success criterion as to whether the new model is working in practice.”
Ms White added that Ofcom is "very directly holding Openreach to the fire" and will judge the success of recent governance changes on whether the investment in fibre broadband actually materialises.