The Deputy Prime Minister has denied that the national alert system being tested on Sunday is an example of nanny state interference.
Oliver Dowden conceded the loud alarm that is due to ring on millions of mobile phones at 3pm would be “a bit inconvenient and annoying”, as well as “irritating”.
But he said the warning system was not an over-reaching of the state as it “could be the sound that saves your life” in the future.
He told Sky News’ Sophy Ridge On Sunday programme that during that local test, which covered a section of the M4 motorway, there “wasn’t any panic at all” among recipients.
Every device using the 4G and 5G networks would be part of a trial on Sunday of a system designed to warn the public if there is a danger to life nearby, with a loud siren due to sound for about 10 seconds.
Once established, the system is intended to be used in life-threatening situations including flooding and wildfires.
“If you look at countries around the world, whether it is the United States, Canada, Japan and elsewhere, they have emergency alerts on phones as another tool in the toolkit of keeping people alerted during an emergency.”
Mr Dowden said the test of the system was a “bit like when the fire alarm goes off at work”.
“It’s a bit irritating at the time but in the future people could be grateful for it because in a real emergency, this could be the sound that saves your life,” he told Sky News.
The senior Conservative reminded the public that it was “just a test” and no reaction was required, other than dismissing the notification.
People who do not wish to receive the alerts will be able to opt out using their device settings, but officials hope the life-saving potential of the messages means users will keep them on.
Phones that are off or in airplane mode will not receive an alert.
The Cabinet Office said the siren-like sound would be no more prominent than the loudest ringtone setting on a mobile.
Phone users would be prompted to acknowledge the alert by swiping or clicking the message before being able to continue.
The test message will say: “This is a test of Emergency Alerts, a new UK government service that will warn you if there’s a life-threatening emergency nearby.
“In a real emergency, follow the instructions in the alert to keep yourself and others safe.
“Visit gov.uk/alerts for more information.
“This is a test. You do not need to take any action.”
The entertainment and sport sectors have been planning how to guard against disruption to large events when the test goes off.
Organisers of the World Snooker Championship will pause play just before 3pm at the Crucible in Sheffield and it will resume after the alert.
The Society of London Theatre (Solt) said it had shared the Government’s guidance with its members and advised them to tell attendees to turn off their phones to “minimise disruption to shows”.
Harry Potter And The Cursed Child, Frozen, Mamma Mia! and The Lion King are among the shows putting on matinees on Sunday.
The test on St George’s Day coincides with major events including the London Marathon and Premier League ties between Bournemouth and West Ham, and Newcastle and Tottenham Hotspur, kicking off at 2pm.
Officials said they had worked with the Football Association and the marathon’s organisers to make sure the impact of the test would be limited.
Drivers have been warned it will still be illegal to pick up their mobiles during the test, and domestic violence campaigners warned the alert could put people in danger by revealing the location of secret phones hidden by those at risk.
The AA said motorists may prefer to switch off their electronic devices before Sunday’s test as laws banning the use of handheld phones will still apply.
Drivers caught holding a phone behind the wheel face six penalty points and a £200 fine.
The National Centre for Domestic Violence warned people with hidden mobile phones to turn off the alerts to avoid revealing the location of the devices.