Thousands of EE and BT customers have reported they are unable to make or receive calls as the mobile phone network faces an outage.
Outages tracker Downdetector, which relies on self-reported user data, showed over 2,500 EE customers experiencing outages at 1400 BST, with many also reporting issues with other networks.
However, Vodafone and Three have confirmed to the BBC they do not have network issues.
A spokesperson from BT, which owns EE, apologised and said the firm was “currently addressing an issue impacting our services”.
“We’re working urgently to fix this issue and will provide a further update as soon as possible,” they said.
Other networks have seen spikes in reports of outages on Downdetector – but these are likely to be customers from networks unable to connect to EE or BT phone numbers.
Social media users have been posting about a loss of services of both EE and BT mobile and landline services.
BT Group has more than 30 million customers in the UK and made £20.4bn revenue in the last financial year.