People can once again call 999 in an emergency after services were hit by a nationwide technical fault.
BT said it had implemented a back-up platform after issues with 999 calls connecting were reported on Sunday morning.
Emergency services across the country have confirmed they are able to receive 999 calls again, but some warned they were still experiencing residual difficulties.
A spokesperson for BT said: “Early this morning we experienced a problem with the 999 service.
“The situation is fast-moving as we fix the problem and our back up platform is now working – so people should call 999 as usual.
“We will provide updates as the issue is resolved.”
Cheshire Fire and Rescue Service warned of a 30-second delay to connect to 999, while Suffolk Police said its system may not be working to full capacity and urged people to use 999 only in a genuine emergency.
The Metropolitan Police said the back-up system was “not as effective at telling us where you are calling from”.
“Help us by having the address of the emergency ready,” the force said.
“If you don’t know the address, look around for a street name or obvious landmark.”
East Midlands Ambulance Service (EMAS) said that if a 999 call was not successful, people should call 111 for urgent medical help instead.
Richard Lyne, strategic commander at EMAS, said: “We urge people to seriously consider the alternative services available and if it’s possible to make your own way to a treatment centre.
“For example, if a relative or friend can take you by car.”
Problems with the service, which is managed by BT, were first reported at around 8.30am on Sunday and people were told to call 101 in an emergency for police and fire, or 111 in a medical emergency.
Several police forces and fire and ambulance services said they were facing issues and said BT had reported a “system failure”.
