Mobile phone users across the UK are reporting issues with voice calls failing to connect, particularly when made between networks.

O2 and Three have confirmed that there have been problems with their own networks and said they were investigating the issue. EE said the problems only occurred during calls to other networks, and intra-EE calls should be fine.

In a message on its website, O2 said it was aware that “some customers may be experiencing issues when making and receiving voice calls on our 2G, 3G and 4G networks” and apologised to customers. Three UK also confirmed an issue with voice calls, which it said was affecting about 3% of customers.

One O2 user reported failing four times to call a contact on Three’s network, only for the call to work first time when made the other way round.

O2 described the problem as “a cross-industry issue”, while EE said it was “an issue in another operator’s network” but did not name a specific operator.

A spokesman for Three UK said: “We are aware of an issue affecting around 3% of voice calls. We apologise for any inconvenience and our team is working to fix this ASAP. The rest of the network is stable.”

The fault comes as millions of people begin working from home as part of government guidance to reduce social contact to help stop the spread of coronavirus. According to Down Detector, a network-status monitoring website, users of all four of the UK’s major networks have reported issues.

“This is not related to the increase in home working caused by coronavirus,” said EE.

Disruption to other technology businesses has come from coronavirus-related spikes in demand, however. Microsoft’s remote-working tool, Teams, suffered login issues on Monday and Tuesday mornings, as a wave of newly remote workers across Europe all logged in at once.

At the weekend, a similar problem affected other industries: Xbox Live went down for many video gamers. “Usage is up on almost everything,” said the head of Xbox, Phil Spencer.

The voice-call issue comes on a day that was supposed to be celebratory for the networks: for the first time, travellers on some underground sections of the London Underground have permanent phone reception, following a successful upgrade by TfL.

The service is limited for now, only affecting passengers using the 1999 extension that forms the eastern half of the Jubilee line. It was implemented at a cost of £10m, and TfL plans to extend the service to the entire line by the end of the year and other lines from 2021.