UK communications regulator Ofcom said it fined BT GBP 42 million for paying its wholesale customers inadequate compensation for late delivery of broadband lines.
The company must also compensate the companies affected and BT estimated that this will total around GBP 300 million.
Ofcom cut the fine by 30 percent after BT admitted full liability but added an additional GBP 300,000 penalty for failure to provide the watchdog with proper information throughout its investigation.
Ofcom said that between January 2013 and December 2014, BT unfairly used a reduced compensation procedure to cut the level of payments to telecoms providers for late delivery of ethernet services by its infrastructure arm Openreach.
BT agreed earlier this month to spin Openreach off into a separate legal structure after sustained pressure from Ofcom, which had threatened the company with tougher regulatory oversight if it refused to comply.
BT usually has 30 working days to comply with a request for ethernet services, the most common type of dedicated, high-speed cables used by mobile and broadband providers, to transmit data and provide vital, high-capacity links for large companies hospitals and schools.
BT, which said the fine and anticipated compensation do not affect its financial outlook, fully apologized for the late delivery of lines.
The regulator opened the investigation in November 2015 after Vodafone complained that BT delivered services late without its consent and provided inadequate compensation.
Under the terms of delivery of such lines, BT is allowed to assume that its wholesale clients have agreed to a deadline extension if it encounters problems that cause a delay but Ofcom found that BT did this retrospectively over a sustained period in order to reduce the level of compensation it owed to telecoms providers.
It said that this behaviour harmed both telecoms companies and their business and consumer end users.
BT is required to compensate the telecoms providers affected within twelve months.
