“We're working on fixing the problem and we'll provide an update once we've discovered what is causing the fault,” the company said in a message to customers.
“We're sorry for any inconvenience caused.”
Some of the worst hit areas was Barnet, Maida Vale, Parsons Green and Maidstone in Kent.
People took to social media to complain of being left with no phone or internet usage for three hours.
One Twitter user called Jenni, who had no connection in her home in Barnet, said: "Hope we're going to be reimbursed for this? Sick of paying for a service and not receiving it. Only just recently switched to Sky.”
David Emin wrote: "That has messed up my Game of Thrones marathon on my day off! What compensation are Sky offering?"
