Ofcom Probe BT and Three UK Over Outages of Mobile Calling and 999 UPDATE2
The UK telecoms and media regulator, Ofcom, has this morning launched fresh investigations into mobile network operators EE (BT) and Three UK following network outages in the summer that resulted in UK-wide disruption to mobile call services, including to emergency services (e.g. 999 for police, fire, ambulance etc.).
The regulator’s existing General Conditions rules (e.g. General Condition A3.2 and sections 105A, 105C and 105K of the Communications Act 2003) require every communications provider to “ensure the fullest possible availability of public communications services at all times, including in the event of a disaster or catastrophic network failure, and uninterrupted access to emergency organisations.”
Suffice to say, any failure of such systems, particularly to the emergency services, is extremely serious due to the risk that it could result in a loss of life. This is particularly relevant now that broadband ISPs are increasingly switching away from traditional landline phone services and on to IP-based digital phone alternatives (inc. VoIP), which may be more exposed to connectivity problems, power cuts and complexities around location reporting etc.
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The issue has already been underlined on several previous occasions, after a string of broadband and VoIP providers, including BT, Gigaclear and Vonage, were hit with Ofcom fines over related failings (here, here and here). The disruption BT’s network suffered in 2023 is particularly notable, given today’s news.
Fast-forward to today and BT has now notified Ofcom of a “software issue” that resulted in a UK-wide disruption to mobile call services interconnecting to and from EE’s mobile network on 24th and 25th July 2025. “This resulted in BT and EE customers being unable to make or receive mobile calls to other networks and emergency services,” said Ofcom.
Separately, Three UK has notified Ofcom of an incident that resulted in a UK-wide disruption to call services on 25th June 2025, including customers’ ability to contact emergency services. “Our investigations will seek to establish the facts surrounding these incidents and asses whether there are reasonable grounds to believe that BT and Three have failed to comply with their regulatory obligations,” said Ofcom.
A BT Group spokesperson told ISPreview:
“We are aware that Ofcom has begun an investigation into the technical fault impacting voice calls on our network on 24th and 25th July 2025. We will co-operate fully with Ofcom throughout the investigation and apologise again for any issues caused by this incident.”
Such investigations can take a bit of time to run their course, so we might not learn the final outcome until later in 2026. But past evidence suggests that BT and Three UK may be likely to face a sizeable financial penalty.
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The BT (EE) Investigation
https://www.ofcom.org.uk/../investigation-into-bt-following-voice-service-interconnect-outages-on-24-and-25-july-2025
The Three UK Investigation
https://www.ofcom.org.uk/../investigation-into-three-following-voice-service-outage-on-25-june-2025
UPDATE 10:01am
We’ve added a comment from BT above.
UPDATE 16th Dec 2025 @ 12:26pm
We’ve added a comment from Vodafone and Three UK below.
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A Spokesperson for VodafoneThree said:
“Three experienced disruption to voice services following an exceptional spike in network traffic triggered by a third-party software configuration change. Since the outage, we have engaged openly with Ofcom and will continue to cooperate fully with their investigation”.
Mark is a professional technology writer, IT consultant and computer engineer from Dorset (England), he also founded ISPreview in 1999 and enjoys analysing the latest telecoms and broadband developments. Find me on X (Twitter), Mastodon, Facebook, BlueSky, Threads.net and Linkedin.
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Most people I know seem to be ditching their landlines altogether especially when switching to FTTP so the mobile networks need to be robust for emergency situations.
It’s certainly an issue in rural areas where power cuts are quite common, our FTTP fails about 1 hour after our nearest village loses electricity, I assume the backup batteries in the cabinet only have 1 hour duration. The mobile phone signal however is lost instantly, the cell site appears to have no backup power whatsoever. At this point a village of 300+ residents has no communications whatsoever due to a single power cable failure..
Openreach FTTP is served from exchanges with generator backup – so the FTTP will (should) stay up indefinitely, so long as you can power your NTE and router at home. Openreach FTTC is battery backed up in the cabinets – more than an hour, about 4 to 6 hours I believe.
although this article has nothing to do with localised faults, and in BT’s case may also have impacted PSTN landline users:
whose FTTP are you referring to, as there will be huge differences between providers. Openreach will (almost always) have their kit in an exchange with both battery and generator backup, whereas some altnets have cheaped out and rely on a few batteries in a cabinet.
Just a thought: Some people in low-signal areas may have installed and forgotten about a cellular amplifier. If that’s not battery-backed in the house, then cellular service is instantly degraded or impossible. The distant tower might be working OK for several hours, but there’s no usable service inside the home.
EE broadband has a sytem that connects your router to EE mobile network in the event of loss of connection to the network, only if you have the rquired kit fitted and a mobile signal available inside your property ( note i said network not mains electricity supply ) say if an underground cable is cut for example your home service will automatically switch to the EE mobile network as a backup. Surely this could automatically cause hundreds of connections to activate thereby causing a sudden serge and a resulting drain on resources, in a localised aerea.
The connections are always active, just not passing traffic. The available bandwidth is limited compared to the broadband connection.
That’s right, if lots of homes have the mobile backup, and there is a total loss of broadband for the whole area, not just a single home or a group of homes, then the mobile backup would not be sufficient to handle meaningful broadband replacement. Phone calls would be prioritised over data, but the local mast would be pretty overloaded for data. The mobile backup solution for Broadband is not meant for that sort of failure, it is aimed at localised failures, ie, your home or business losing Broadband. In this thread the loss of mobile is more likely, as Broadband is more likely to survive a powercut (owing to exchange batteries/generator) than the mobile tower, as only a small percentage of mobile towers have power backup.