O2 UK isn't having a good day today: The Telegraph reports that many customers of the mobile phone operator (and its subsidiaries GiffGaff and Tesco Mobile) have had difficulty using data or sending and receiving calls and text messages. The Telefónica-owned carrier doesn't have any explanation of what has caused today's problems, nor has it offered any estimate of when service will be fully restored. O2's service status page says that problems have been occurring since 1:30pm local time and that "Our engineers are dealing with the problem as a priority and we hope to restore full service as soon as possible." Since it's nearly 8pm in the UK at the time of this writing, it's clear that there's a major issue that engineers are having trouble to rectify. Full statement from O2 below:

We continue to manage the problem on our network that is affecting some of our customers. Customers may still be having difficulty making and receiving calls, sending texts or using data. We are sorry for any inconvenience. Our engineers are dealing with the problem as a priority and we hope to restore full service as soon as possible

Thanks, Gladmo2!

Update: The issue has now been resolved — and it may have affected a full third of O2's users.