O2's network has been fully restored after a data outage affecting up to 32m customers lasted the entirety of Thursday.
Problems were first reported at around 5.30am yesterday, with O2 customers saying they could not use 3G or 4G data.
The error also took down Giffgaff, Sky's mobile services, Lycamobile and Tesco Mobile, which all rely on O2's network, meaning up to 32m people were affected.
"We can now report that our 4G network has been restored," an O2 spokesperson said overnight, with the fix coming at around 3.30am this morning, after restoring 3G at around 9.30pm yesterday.
"Our technical teams will continue to monitor service performance closely over the next few days to ensure we remain stable.
"A review will be carried out with Ericsson to understand fully what happened. We’d like to thank our customers for their patience during the loss of service on Thursday 6 December and we’re sorry for any impact the issue may have caused."
Mark Evans, chief executive of O2, said the outage was caused by a "global software issue" experienced by Ericsson, which supplies IT services to the network giant.
"I want to let our customers know how sorry I am for the impact our network data issue has had on them," Evans said.
Outage Update: Our teams are working closely with one of our 3rd party suppliers who has identified an issue in their system which has impacted mobile services globally. This is our top priority and we are really sorry. Get updates here: https://t.co/5oS7qap2bj
— O2 in the UK (@O2) December 6, 2018
Downdetector, a website that tracks digital outages, said 1,662 complaints had been made before 7am, with the outages affecting London, Birmingham, Manchester, Glasgow, Leeds and many other towns and cities.
The outage had knock-on effects for systems reliant on O2's network, such as Transport for London's electronic bus timetable, which was not working this morning.
Hi Demi. Due to a technical fault bus predictions are unable to appear on Countdown and apps. We are working to rectify this issue as a priority. Please check your bus timetable here: https://t.co/KBuRJW9YKT Thanks, Tom.
— Transport for London (@TfL) December 6, 2018
Angry users took to Twitter to look for answers or to simply vent their anger.
O2 directed users to a status checker to see whether their local network was affected.
It comes after BT Mobile customers also suffered a network outage. BT Mobile customers said they couldn't send or receive text messages, after first reporting problems yesterday. BT later resolved the problem.