Ofcom has opened an investigation into BT and Three after mobile network outages disrupted services across the UK. Some users also struggled to reach emergency 999 services.
In June, thousands of Three customers reported problems making calls. A similar outage affected BT and EE customers in July. Ofcom will review whether the networks took enough steps to prevent these failures.
Both companies have responded to the regulator. Three said it is working closely with Ofcom. BT Group apologised to customers and confirmed it will cooperate fully with the investigation.
BT said it regrets the disruption caused by the incident. Three explained that a sudden surge in network traffic triggered the outage. A third-party software configuration change caused that spike.
Three added that it has remained open with Ofcom since the incident. The company said it will continue to assist the investigation.
Ofcom said telecoms providers must actively identify risks to their networks. It added that companies must also reduce harm when problems occur.
Telecoms analyst Paolo Pescatore said reliable connectivity remains essential. People expect strong connections at home and while travelling. He noted that outages can still happen despite safeguards. However, companies must spot faults quickly and prevent repeat issues.
The incidents caused widespread disruption. On 25 June, three confirmed problems were identified with making and receiving calls. The issue also affected networks that rely on Three’s infrastructure, including ID Mobile.
A month later, similar complaints came from BT and EE customers. At the time, the government reminded providers of their legal duty. Operators must keep networks resilient, especially for emergency access.
The investigation follows earlier enforcement action. In July 2024, Ofcom fined BT £17.5 million. A serious system failure stopped thousands of emergency calls from connecting.
Three has also faced penalties in the past. In 2017, Ofcom fined the company £1.9 million. The regulator said Three could have prevented a major service outage.
Three has since merged with Vodafone. The combined company now serves about 27 million customers. The current probe will test how large networks manage risk as demand grows.
