UK regulator Ofcom started investigations into BT and 3 UK following outages earlier this year, which caused disruption to mobile calls including to emergency services.

The watchdog stated the BT issue occurred between 24 July and 25 July, with the company informing it of a software issue resulting in UK-wide disruption to mobile call services interconnecting to and from its EE network.

The problem resulted in customers being unable to make or receive calls to other networks and emergency services.

A similar incident occurred for 3 UK, resulting in a UK-wide disruption on 25 June.

Ofcom explained operators are required to take appropriate and proportionate measures to identify and reduce the risks and prepare for the “occurrence of anything that compromises the availability, performance or functionality of their network or service”.

It added: “Our investigations will seek to establish the facts surrounding these incidents and assess whether there are reasonable grounds to believe that BT and Three have failed to comply with regulatory obligations.”

BT stated it will fully cooperate with Ofcom throughout its investigation.

Ofcom hit BT with a £17.5 million fine in July 2024 for what it described as a “catastrophic failure” of its emergency call handling services.

3 UK was last hit with an Ofcom fine in 2017, when it was ordered to pay £1.9 million over a network issue.

The operator has merged with Vodafone UK, with a deal between the pair completing at the end of May. However, Vodafone was not mentioned in Ofcom’s statement.