The test takes place at 3pm
Further details have been released about the alert that will be sent to smartphones on Sunday, to test a new public warning system.
A message with a siren at 15:00 BST on 23 April will say “in a real emergency, follow the instructions in the alert to keep yourself and others safe”.
It will give a sound and vibration for 10 seconds even for phones on silent. Phone users will have to acknowledge the alert before they can continue using their devices. It is being sent to 4G and 5G mobile phones.
The alert system will be used to warn of extreme weather events, such as flash floods or wildfires. It could also be used during terror incidents or civil defence emergencies if the UK was under attack.
People at risk of domestic abuse have been advised to turn off any mobile device they want to keep hidden. The government has stressed that the alarm will not sound if the phone is switched off or put on airplane mode.
For further details, see the BBC website