O2 has been hit by a computer problem that has resulted in customer service staff being unable to access account details for as many as 400,000 customers.

The glitch outage occurred at around 4.00am this morning, affecting part of the customer service platform. Engineers are working to resolve the problem, but at this stage O2 has no idea when it will be fixed.

A spokesman for the mobile operator - which has 11.2m users in the UK - said the glitch does not impact customers' ability to make or receive calls. ®