Mobile operator O2 is still trying to get its service up and running again after a system crash left hundreds of thousands of customers without network coverage.
The problem started yesterday afternoon, leaving some users unable to make or receive calls, send texts and access data services.
In a statement released earlier today, the company confirmed that a network fault was to blame.
"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," said the company in a statement.
"We, and our central supplier, have deployed all possible resources and [have been] working through the night to restore service as soon as possible."
At the time of writing, the company released a follow-up statement announcing that its 2G services were operational again and that its 3G network was "starting to restore".
This should result in a "gradual return" of normal mobile data services over the course of today, the statement said.
"Customers affected may wish to try switching their mobile phones off and on as service returns," it added.
The outage also affected Tesco Mobile and Giff-Gaff customers, which are mobile virtual network operators that make use O2's services.
The latest outage follows on from another failure two weeks ago where O2 users were unable to text for 24 hours.
