The chief executive of O2 UK, Ronan Dunne, has apologised for the problems that left thousands of customers unable to use its services for the last 24hrs.
He told Sky News that he was embarrassed by the network failure and that O2 would "make it up to our customers and make sure it doesn’t happen again".
Mr Dunne added: "Let me reassure you we will redouble our efforts to get to the bottom of this."
Thousands of disgruntled O2 customers took to Twitter this morning to vent their frustration at still being unable to use their phones.
Thousands of customers face a second day of disruption with O2's mobile network, despite reassurances that it has been partially restored.
Thousands of O2 customers across the country were still unable to use their mobile phones today.