The communications regulator, Ofcom UK, looks set to reconsider demands for BT to offer a Dark Fibre product when it begins reviewing the business connectivity market later this year. BT has always been opposed to such a move because doing so would threaten its lucrative Leased Line market (Private Circuits that provide a full-time, dedicated and direct connection between two sites).

Dark Fibre usually references a high capacity fibre optic cable that has been laid by an operator, such as BT, but is not presently being used. This might seem unusual but it's actually very normal and often stems from a desire to save money by deliberately building extra capacity for future growth.

Several business ISPs already offer Dark Fibre, including BT, although crucially these are usually only provided for corporate purposes and rarely to help serve the country's growing domestic needs.

The European Commission (EC) is also on-record (Digital Agenda) as calling for ISPs to be given access to dark fibre alongside the more familiar but separate goal of forcing incumbents to open up their cable ducts and telegraph poles through Physical Infrastructure Access (PIA).

However it's unclear precisely how much Dark Fibre BT actually has to play with. Last year's Wholesale Local Access Review by Ofcom suggested that the operator had "very little dark fibre deployed in the access network," even in large metropolitan areas.

According to Br0kenTeleph0n3's Ian Grant, BT has over 8 million kilometres (km) of fibre installed (this is growing rapidly as its superfast FTTC and FTTP broadband rollout expands ever closer to homes) and a colossal 121 million km of copper.