The mobile network Three say a major outage which affected its services on Thursday is fixed, but have warned of further problems due to Storm Éowyn.
Customers told the BBC they couldn’t make 999 calls during the interruption.
The firm has apologised after more than ten thousand people told outage tracker Downdetector they were unable to make or receive phone calls.
There were also been several thousand reports from users of Smarty and ID Mobile – smaller mobile companies which use Three’s network.
A Three spokesperson said: “Following an issue affecting voice calls yesterday, services have returned to normal overnight.
“We continue to monitor and review all services throughout today to ensure full stability.
“However, today we expect to see an additional impact on our service due to Storm Éowyn in some areas.”
The spokesperson said extra engineering resources had been deployed to deal with any disruption caused by the storm, which is battering the UK on Friday.
Just after 07:00 on Friday, Downdetector had over 1,300 reports of outages on Three.
The BBC was told by members of the public that 999 calls would not connect from their devices using the Three network.
While the BBC has not been able to independently verify their specific claims, Three has said it received a “small number” of reports of 999 call failures and has launched an investigation.
A spokesperson added: “A normal volume of 999 calls were connected yesterday and our monitoring confirms the service is working fully this morning.
“We apologise sincerely for the inconvenience caused by the issues on our voice network yesterday.”
Three has around 10.5m customers across the UK, according to its website, but it is unclear how many of them were affected by the outage.
Many people on social media shared their frustration and described the disruption they said it had caused them.
One person claimed they had “missed a medical appointment” as a result of being unable to receive calls, while another said the issues had left their daughter “stranded”.
And several people have 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”.
It comes a month after the UK regulator gave the go-ahead for Three to merge with former rival Vodafone in a £16.5bn deal.
Meanwhile, the Three outage occured on the same day a major outage affected artificial intelligence tool ChatGPT.
