The mobile network Three reported that some 999 calls didn't go through during a major outage affecting thousands of customers.
The company stated that the issues with its services on Thursday have been resolved, but warned of potential further problems due to Storm Éowyn.
Many customers contacted the describe the disruption caused by the network failure on Thursday, with some saying they were unable to call 999.
While the BBC has not independently verified these claims, Three informed that it received reports of 999 call failures affecting no more than ten customers and has launched an investigation. A Three spokesperson said, "A normal volume of 999 calls were connected yesterday, and our monitoring confirms the service is fully operational this morning.
"We sincerely apologize for the inconvenience caused by the issues on our voice network yesterday."
More than ten thousand people reported to outage tracker Downdetector that they were unable to make or receive phone calls on Three on Thursday.
There were also several thousand reports from users of Smarty and ID Mobile, smaller mobile companies that use Three's network.
Since 2009, Ofcom has required all UK mobile network operators to allow people to call 999, enabling emergency calls even when users are outside their home network's coverage. If a network is down or has no coverage, emergency calls will connect through any available network in the area.
A spokesperson from Three said: "BT, which operates the 999 service, has confirmed that the call traffic from our network was as expected yesterday.
"Reports from our customers experiencing issues with 999 calls are very few. We are taking these reports seriously and are investigating them."
Impact of Storm Éowyn
Storm Éowyn also caused problems for Three on Friday.
A spokesperson from Three said: "After an issue affecting voice calls yesterday, our services are now back to normal, except for some local issues related to Storm Éowyn. We are very sorry for any inconvenience this caused our customers."
The spokesperson mentioned that extra engineering resources have been deployed to handle any disruptions caused by the storm, which is hitting the UK on Friday.
Just after 08:00 on Friday, Downdetector had over 1,300 reports of outages on Three, but this number has decreased since then. Three also informed that a "very small number" of people connected to WiFi when calling are not getting through on Friday.
According to its website, Three has around 10.5 million customers across the UK, but it is unclear how many were affected by the outage.
Many people on social media expressed their frustration and described the disruption it caused them.
One person claimed they had "missed a medical appointment" because they couldn't receive calls, while another said the issues left their daughter "stranded."
Several people have also claimed they would be leaving the network altogether.
In a statement on Thursday, the regulator Ofcom said it was in contact with the network to "establish the scale and cause of the problem as soon as possible."
It is not known whether customers will be able to claim compensation for the outage, although according to the Ofcom website, it "may be appropriate" for providers to offer refunds "while repairs are being made."
This comes a month after the UK regulator approved Three's merger with former rival Vodafone in a £16.5bn deal.
Meanwhile, the Three outage occurred on the same day a major outage affected the artificial intelligence tool ChatGPT.