Thousands of O2 customers across the UK suffered a mobile blackout for up to seven hours over bank holiday Monday.
The network outage, which affected customers from Glasgow to London, also struck customers on Tesco Mobile, which piggybacks on the O2 network.
Users started complaining about the lack of connectivity in the late afternoon, but it took O2 until 20:22 BST to respond on Twitter that they were aware of the issue.
We’re aware of isolated instances where some customers have intermittent access to our service. We’re investigating and will update ASAP
— O2 in the UK (@O2) May 25, 2015
Tesco Mobile tweeted an hour later that they were aware their customers were also affected
We understand some customers are experiencing difficulties; we're really sorry & are working hard to get this fixed: http://t.co/NU5BZy1bGi
— Tesco Mobile (@tescomobile) May 25, 2015
Full service resumed at 23:35, and O2 said that they have launched a full investigation into what caused the outage.
As the issue only affected a portion of its customers, the mobile phone operator said that it was not offering a blanket refund, but may offer compensation to those affected on a case-by-case basis.