The company responded to a report in The Register that Sky Broadband customers in Doncaster, North Wales and Bristol were being affected by a big slowdown in their speeds.
Sky did not supply any further information on the issues, but said that it was working on boosting capacity at telephone exchanges in the worst affected areas.
"Following a combination of an underlining increase in network traffic as well as a high rate of new customer additions, we are aware of capacity issues in a small number of exchanges," a Sky spokeswoman said.
"We are working on adding new capacity to those exchanges as quickly as we can. We apologise to all customers who have been impacted by this issue."
Some Sky customers in hit ares had reported that their service dropped from 13-14Mbps down to as low as 2Mbps. One man even said that his connection had fallen from an off-peak speed of 16.8Mbps to just 0.8Mbps.
One frustrated customer in Doncaster told the Register: "Internet is completely unusable, so this is the THIRD night in a row that I am unable to fulfil my contractually obligated working from home via the internet, so a third night's overtime lost. Not only is this a pain, it's actually losing me wages."
Sky has provided an online postcode checking service for subscribers to check if their local exchange has been hit by the slowdown issues.
The firm also insisted that less than 5% of its broadband customer base has been affected. But it has not indicated as yet whether those hit by the issues could be offered any form of compensation.
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