BT may be forced to break up its internet broadband business under competition proposals being considered by the communications watchdog.
The telecoms giant is currently required to provide access on equal terms to its competitors though the Openreach fibre broadband network.
Regulator Ofcom said it is reviewing whether splitting Openreach from BT may be the best way to improve competition in the sector.
It follows complaints that the network's performance on behalf of other providers has often been poor, leading to new rules on faster line installations and repairs.
Other possibilities under consideration include retaining the current model or deregulating and allowing different networks to provide services without using BT's network at all.
Virgin Media and some smaller operators currently own their own networks, but Ofcom said this model of "end-to-end" competition could lead to duplication of networks and weak competition.
An Ofcom spokesman said: "Ofcom believes UK consumers are likely to get better services at lower prices if there is a sufficient number of effective competitors."
A BT spokesman said: "We welcome this review and are confident it will find the UK broadband market to be both vibrant and healthy.
"There has been huge progress this past 10 years with an explosion in competition and broadband usage."