Mobile network O2 and telecoms company Ericsson have issued a joint apology after millions of customers were unable to get online.
O2 UK CEO Mark Evans said the company would be working with systems and equipment provider Ericsson “through the night”, and that a full service should be restored by Friday morning.
A later statement from O2 said service was expected to be restored by 3am.
British customers reported not being able to use mobile data to access the internet and the operator’s network on Thursday – which was the result of a technical fault.
Mr Evans said in a statement: “I want to let our customers know how sorry I am for the impact our network data issue has had on them, and reassure them that our teams, together with Ericsson, are doing everything we can.
“We will continue to work with Ericsson, through the night, who have assured us that a full service will be restored for customers by the morning.
“We fully appreciate it’s been a poor experience and we are really sorry.”
On Thursday evening, O2 said 3G data service was returning and that they anticipated it to be fully restored by 9.30pm.
In a statement shortly after midnight on Friday, the company said: “Our technical teams have started to return our 4G service to our network.
“We anticipate this will be restored by 3am this morning, meaning all our services will be fully restored.”
O2, which has more than 25 million UK customers, saw disruption to its network begin at around 5am on Thursday and last for most of the day.
Other mobile networks, including Sky, Tesco and Giffgaff, were also affected by the problem because their networks use O2 services.
The CEO of Ericsson UK and Ireland, Marielle Lindgren, said: “The cause of (the) network issue is in certain nodes in the core network resulting in network disturbances for a limited number of customers across the world, including in the UK.
“We have been working hard on resolving the UK data issue. The faulty software that has caused these issues is being decommissioned.
“Our priority is to restore full data services on the network. Ericsson sincerely apologises to customers for the inconvenience caused.”