According to O2 status site https://status.o2.co.uk/
We’re aware that our customers are unable to use data this morning. One of our third party suppliers has identified a global software issue in their system which has impacted us. We believe other mobile operators around the world are also affected. Our technical teams are working with their teams to ensure this is fixed as quickly as possible. We’d encourage our customers to use Wifi wherever they can and we apologise for the inconvenience caused.
10:21- 6th December 2018
The technical team are still working to resolve the issue with 2G, 3G & 4G calls, texts & data across the UK, we did see a significant increase in website traffic across giffgaff.com and as such we temporarily moved our website over to our outage server.
We can confirm that access to the giffgaff community has now been restored & members will be able to access their account as normal.
We apologise for the inconvenience and thank you for your continued patience.
giffgaff Educator | WFH Team