The Three mobile phone network appears to be down, with customers complaining that they are unable to make or receive calls.
People in some areas, such as Colchester and London, are reporting issues on social media.
The official Three account on Twitter has yet to announce any issues.
According to the website DownDetector, people began to notice the problems at approximately 5:48am GMT – with more people reporting them at around 8:00am GMT, when the work day would begin.
More to follow.