The problems seem to have started at around 8:00 AM this morning and are ongoing at the time this article was posted.
"Our technical teams are investigating reports of issues when using data", O2 wrote on its status page. "We apologise to our customers for any inconvenience".
Other mobile networks, including Sky, Tesco and Giffgaff have also been affected by the problem because their networks use O2 services.
Angus Council say its meters have been affected by a network problem affecting all of the UK.
China to 'immediately' implement USA trade truce measures
Beijing, for example, didn't mention the 90-day deadline for talks on a deal over technology issues. But the Chinese statement on this weekend's meeting only said Beijing agreed to buy more USA goods.
Ofcom says that if your provider fails to fix a fault by the date promised, or you are unhappy with how long it is taking, you should follow their formal complaints procedure.
O2 have assured customers that they are working as hard as possible to get the networks up and running as soon as possible.
The outage also has serious implications for places that rely upon the O2 network for real-time informational services, as reported by the Independent.
O2's data network has gone down, leaving users unable to access the internet.
An O2 spokesperson said the network was continuing to investigate the problems.
In addition, London Bus timetables rely on O2's coverage, meaning that these were also down this morning.