It is estimated that hundreds of thousands of O2 customers could not use their mobile phones after the network crashed yesterday afternoon.

Many mobile users are unable to make or receive calls and text messages.

Today, O2 announced that it had restored its 2G service, but was still working on 3G.

A spokeswoman said: “We can confirm that the problem with our mobile service is due to a fault with one of our network systems, which has meant some mobile phone numbers are not registering correctly on our network.

“We, and our central supplier, have deployed all possible resources and have been working through the night to restore service as soon as possible.”

She added that it was estimated at least “thousands” of people had been affected.

The company admitted: “Unfortunately we’re unable to confirm any timescales for service restoration at this time. We’ll let you know as soon as we can. We apologise once again for any inconvenience this incident is causing.”

Image: Getty