02 is investigating with "high priority" after its data services went down, with tens of millions of users potentially affected.
The problem is also affecting customers of Sky Mobile, Tesco Mobile, Lyca Mobile and GiffGaff – which all use 02’s infrastructure.
The network said on Thursday morning: Our technical teams are investigating reports of issues when using data.
Voice calls are working OK. Our technical teams are investigating. We apologise for any inconvenience…
Customers tweeted that they were unable to use 3G and 4G services.
Stacey Caine posted: [email protected] come on 02 unable to text anyone all my texts are failing, and no data. Currently using my WiFi.
Andrew Davies said: Where has all the data gone…[email protected] appears to have broken this morning! No mobile access on my phone Good job I have different provider on iPad!
@anthony_vol1 posted: Nice start to today 02 data has gone down, thank God for free Wifi on buses.
Me, my mum and my sister don’t have any mobile data either, we have 30gb showing on our 02 account!! Definitely think they have gone down, tweeted @stephanie_bint.
Nicola Barton said she was heading to Great Ormond Street Hospital when she realised data was down.
Out all day at GOSH for appointments for my daughter and 02 decide today is the day for it’s data service to go down. Fabulous, will rely on intermittent connections to wifi for the day then.
An 02 tweet said: We are aware our customers are unable to use data this morning. Our technical teams are working on the issue with high priority.
We are really sorry and working as hard and as fast as we can to fix this. Please keep an eye on our status checker: http://o2.uk/ServiceStatus .
In London, the electronic timetables at the city’s bus stops was also reported to be not working and is thought to be related to the 02 outage.
(c) Sky News 2018: 02 urgently investigating as data services stop working