The firm said people were still able to use mobile data services and make 999 calls during the outage.

Three’s support team has been telling customers that it does not “have a timeframe” for a fix, but that the firm is “working hard to resolve this as soon as possible”.

Three has around 10.5m customers across the UK, according to its website, but it is unclear how many of them are affected by the outages.

Many people on social media have shared their frustration at the outage and described the disruption they said it had caused them.

One person claimed, external they had “missed a medical appointment” as a result of being unable to receive calls, while another said, external the issues had left their daughter “stranded”.

And several people have claimed, external they would be leaving the network altogether.

It is not known whether customers will be able to claim compensation for the outage, although according to the website of telecoms regulator Ofcom, 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.

It comes the same day a major outage affected artificial intelligence tool ChatGPT.