Engineers are working to fix the issue that has meant customers can not use their mobile data to access the internet and other services on its network.
Regulator Ofcom is responsible for adjudicating if the company is at fault, a spokesperson told the Mirror: "We are aware that O2 is experiencing problems with its network".
BT is removing Huawei equipment from its mobile carrier EE's existing 3G and 4G LTE networks, saying it will also not use the Chinese tech giant for its upcoming 5G network deployment.
O2 says that voice services should not be affected by the outage.
They said: "One of our 3rd party suppliers has identified a software issue in their system".
SoftBank said the outages stemmed from problems at exchanges for its high-speed wireless LTE network, while O2 blamed an issue in a third-party supplier's system that was impacting services globally. Our technical teams are working with their teams to ensure this is fixed as quickly as possible.
According to Ericsson, the issues were within nodes in the core network, which rippled out to affect "a limited number of customers" using particular software versions from the country.
"Our teams, together with Ericsson, are doing everything we can", Telefonica O2 UK CEO Mark Evans added.
"The faulty software that has caused these issues is being decommissioned".
The network outage isn't just forcing British mobile users to put down their phones and talk to one another.
One of the largest United Kingdom phone networks, O2, is investigating a network outage that has rendered mobile data inaccessible to the company's 25 million customers.