The United Kingdom's mobile phone alert system is an emergency population warning system currently in development that uses cell broadcast. Early testing began in 2014, with the first test alert sent in March 2020. The system is intended for use for major crises such as flooding or terror attacks.
During the Cold War, the UK developed an emergency alert system called the Wartime Broadcasting Service, aimed to keep UK residents informed after a catastrophic wartime attack, such as a nuclear warhead detonation or severe bombing.
The state of this system is currently unknown to the public, and most information about it is held exclusively by BBC high-ranking executives and government officials.
In 2013, the Government of the United Kingdom trialled a system similar to other countries in which cell broadcasts would be simultaneously broadcast to multiple mobile devices. The final project report in 2014 found that "Responders remain very keen to see the implementation of a national mobile alert system" and that "the majority of people (85%) felt that a mobile alert system was a good idea." The report said it was the hope to carry out more trials, however past that point no further trials were conducted. An earlier 2012 report ("Extended Floodline Warnings Direct Trial") by the Cabinet Office using mobile phone calls found that only 12% of recipients acknowledged the alert. During the COVID-19 pandemic in the United Kingdom, the government was accused of ignoring its own advice to set up UK emergency alert system and how after seven years of the Cabinet Office's own report showing such systems were successful, there was "no sign of a system being developed."
In March 2021, a test across all networks on the test channels took place in Reading with the British government's Flood Information Service updating a page on its website, stating that the new cell broadcast system is being tested, and some devices may receive test alerts. This page was updated again in April for further operator tests.
A test broadcast was made for customers on O2 on 11 May 2021 at around 8 am to users who had enabled test alerts in their phone's Wireless Alerts settings. A similar trial was run on the 20 May for EE customers. Two alerts were sent, received at around 13:21 and 13:48 respectively.
The first test on the public channels for the new Emergency Alerts System was on the 25th of May in East Suffolk, the second test of the system was on the 29th of June in Reading, before being rolled out with an introduction Emergency Alert nationwide in early 2022. The system is guaranteed to work on iOS 14.5 and later, and on Android 11 and later, though if Wireless Alerts settings are available on older Android devices, the alerts are very likely to work on those, too. Since the majority of Android devices are already compatible with Cell Broadcast alerts such as the USA's WEA system, most older Android devices should also be compatible.
The alerts will only be available on devices that connect to the UK's 4G and 5G networks, and not 2G or 3G, despite Cell Broadcast being part of the GSM specification since before 2G adoption was widespread in the UK.
On 26 December 2021, the government sent another nationwide text message to inform the population about the availability of COVID-19 booster vaccinations, available for free through the NHS.