EE says it has fixed a technical problem that affected internet services for customers.
The network said “some” customers had been affected, and the website Down Detector said it had received more than 1,000 reports of problems since shortly before 8am on Tuesday.
The issue appeared to be mainly affecting London, Birmingham, Bristol, Glasgow, Manchester, Hackney, Nottingham, Harrow, Hounslow and Leeds, according to Down Detector.
An EE spokesman said: “We’ve fixed a technical issue that affected mobile internet services for some of our customers this morning.
“All services are now being restored for our customers and should be back to normal soon.
“If customers are still unable to connect, they can try turning their phone on and off again, or toggling flight mode on and off, and that should help restore data services.
“We’d like to thank our customers for their patience while we fixed this issue, and we apologise for any inconvenience.”
EE customers reacted angrily to the outage, with many saying they had received no information from the network.