Mobile operator O2 has said it will compensate its customers following a day of disruption to its data networks.
Customers with a monthly subscription will be refunded the cost of two days’ service by the end of January.
Pay As You Go customers will get 10% extra when they top up their phone in the new year or 10% off when they buy data for mobile broadband devices.
On Thursday, O2 issued a joint apology with mobile network equipment supplier Ericsson for the shutdown.
The compensation for customers on monthly subscriptions includes small businesses and mobile broadband users.
Business customers are advised to contact their O2 corporate account manager to discuss compensation.
O2 has 25 million users and also provides services for the Sky, Tesco, Giffgaff and Lycamobile networks, which have another seven million users.
Services such as bus timetable information were also affected, while many businesses faced disruption.
What caused the problem?
Ericsson president Börje Ekholm said “an initial root cause analysis” had indicated that the “main issue was an expired certificate in the software versions installed with these customers”.
The company was carrying out “a complete and comprehensive root cause analysis”, he added.
O2 said voice calls were not affected by the problem, but some customers said they could not make calls or send texts either.
O2 is owned by Spain’s Telefonica and has the UK’s second-largest mobile network after EE, which is part of BT. It is the company that bills customers, so it holds the responsibility for compensation.
Mr French, of Which?, said the company should “do the right thing” for customers, with the option of offering additional perks alongside refunds.