The market opened lower, with BT Group down after regulator Ofcom ordered it to legally separate from Openreach.
In early trading, the benchmark FTSE 100 index was down 33.66 points, or 0.5%, at 6,765.81.
BT shares were down 1.4% after Ofcom said it would notify the European Commission of its plans to force the legal separation of Openreach, which runs the UK’s broadband infrastructure.
Ofcom said BT had failed to voluntarily address competition concerns.
The regulator wants Openreach to become a distinct company with its own board, with non-executives and a chairperson not affiliated with BT. However, it has resisted calls to split Openreach off entirely.
Ofcom had originally called for Openreach to become distinct company within BT in July.
“Ofcom isn’t really saying anything radically different today in terms of the actual meat of the changes,” said Neil Wilson, from ETX Capital.
“What’s concerning investors is the detail of the separation, such as the transfer of pension liabilities and budget autonomy – BT’s pension black hole has ballooned to top £10bn and this is a concern for investors.”
Elsewhere on the FTSE 100, mining shares were among the biggest fallers, with Anglo American, BHP Billiton and Rio Tinto all down by more than 2%.