Virgin's internet service appears to have stopped working, with people unable to get online.
The company's mobile data service appears to have broken for at least some users, who are unable to make calls or get online.
The issues started around lunchtime, according to the website Down Detector. They were reported across the country, it said.
While the Virgin Media Twitter account has been hit by a huge number of complaints, it has yet to respond to the problems publicly.
It said sorry to those users who were affected and complained in direct messages.
"We’re working quickly to resolve an issue that’s affecting some of our customers making calls, sending text messages and using mobile data. We apologise to our customers for the inconvenience caused," the posts read.
The company was sending the apology post to numerous users each minute, as a run of complaints flooded in.
It comes after the company was found to be worst in the country for internet outages. Researchers last month said one in six Virgin households found themselves without internet for hours or days at a time.
If internet outages last for long enough, users may now receive refunds from their internet companies. At the beginning of April, various internet providers signed up to an Ofcom scheme that will allow users to get automatic payments for long-lasting problems.
