The latest update from O2 was posted on their website at around 1am, saying that service had been 'fully restored'. This morning some customers are still complaining about a lack of service:
Further to our previous update where some customers in some areas were unable to make or receive calls, send texts or use data, service has now been fully restored for all remaining impacted customers.
Our engineers continue to monitor the situation through the night. Customers still experiencing issues should try to power the phone off and on. Once again we’re sorry for any inconvenience this has caused.