Sky said in a submission to telecoms regulator Ofcom on Monday that it believed a history of under-investment in BT's infrastructure business, Openreach, had led to problems such as network faults and long waits for new lines to be installed. Openreach operates and maintains Britain's telecoms network.
Sky said it regarded the issues it raised as sufficient for Ofcom, which is itself carrying out a review of the sector, to ask the Competition and Markets Authority (CMA) to conduct an inquiry into BT's Openreach division.
Rivals Sky and TalkTalk have stepped up their charge against BT ever since it announced its planned acquisition of EE, Britain's biggest mobile operator, at the end of last year.
In March, the two firms asked Ofcom to break up BT, requesting that Openreach be spun off.
Ofcom said on Monday that it was carrying out an overarching review of the communications market, including questions around structure and competition.
"We welcome evidence and analysis from all parties to help inform that work, and we will publish an update later in the summer," a spokeswoman said.
Sky said Openreach has missed over 5,000 appointments each month to install new lines for its customers, which represents a third of broadband users on the network, and failed to complete a further 4,000 jobs per month.
BT said Sky was engaged in "selective spin".
"We acknowledge there is more to do on customer service but breaking up BT is not the answer," said a spokeswoman.
"It would lead to huge uncertainty and fundamentally undermine the case for future investment dragging the UK backwards at the very time it needs important investment in its infrastructure," she added.
© Thomson Reuters 2015