The UK's communications watchdog has hit Three with a £1.9m fine after discovering a failure in its systems could have left customers unable to call the emergency services.

Mobile operators are obliged to have a back-up system that means customers can call emergency numbers such as 999 even if there is a problem with the network.

Ofcom discovered Three breached the rules in a way that had a "potential impact on public health and safety".

It found the problem after Three reported a temporary loss of service in Kent, Hampshire and parts of London last year. Ofcom's investigation following the issue revealed Three hadn't sufficiently secured its emergency line.

Ofcom found all of Three's emergency calls from customers in the affected locations were being directed through one data centre. A problem with this data centre could have left customers unable to call 999 and other emergency numbers.

"Three's network should have been able to automatically divert emergency calls via back-up routes in the event of a local outage," said Ofcom. "But these back-ups would also have failed because they were all directed through this one point."