O2 has confirmed problems with mobile data across its network this morning (Thursday, December 6, 2018).
Thousands of angry customer have been complaining to the mobile network since the problem started at around 6am this morning.
Companies that share its network – such as GiffGaff, Sky Mobile and Tesco Mobile – are also being hit by the problems.
In a message on Twitter, O2 said: "We are aware our customers are unable to use data this morning.
"Our technical teams are working on the issue with high priority.
"We are really sorry and working as hard and as fast as we can to fix this."
The company has confirmed that voice calls are still working, and have asked customer to alert them to any network issues they may be experiencing.
Many users will have received an alert to their handsets warning of the drop in service.
Some users also suggested that SMS messaging might not be working, too, leaving them unable to send texts.
You can check the network status as well as receive live updates directly from 02 here