The UK will hold its largest home defence exercise in decades next year to better prepare the country for the possibility of war.
Dubbed "Operation Albiston Shadow", the Cabinet Office said the scenario will likely involve ministers as well as hundreds of officials from across government and the public sector.
It will test responses to "hybrid" attacks under the threshold of conventional war.
The kind of threats that will be simulated were not mentioned, but they could involve cyber attacks, sabotage or assassinations.
The wargame will run across a number of days and will complement a wider NATO exercise.
In a major update on the UK's defence and resilience planning, Darren Jones, chief secretary to the prime minister, also revealed that a new campaign will be launched later this year to raise public awareness about the importance of national resilience.
In addition, his department published an update to a national risk register - which tracks the various risks to the UK, from all-out war and cyberattacks, to droughts and pandemics.
For the first time, the risk of interference in the UK's democratic process has been added to the register along with six other threats, including the potential for artificial intelligence to facilitate more sophisticated cyber attacks on data infrastructure, water infrastructure and police systems.
"Throughout our history, the UK has overcome challenges from plagues and pandemics to war and our fair share of wet weather," Mr Jones said in a written statement.
"It is right that we consistently evaluate the risks we could face and plan for what may come.
"This year, we saw temperatures across the UK breaking records in May, only to be exceeded again in June, and AI offers new ways for criminals to carry out cyber attacks against us, as well as offering huge opportunities for our economy and security.
"The government will do all it can, and we are well prepared - but we can all play our part to keep ourselves and our loved ones safe.
"This campaign will help the public to take small but important steps to be prepared in case of emergencies and disruption - be that severe weather or a cyber attack, which can impact access to power, water, or phone signal.
"Being prepared not only helps people keep themselves and their families safe, but also means the emergency services can focus on helping the most vulnerable in communities."
Against this backdrop, Mr Jones said the government is accelerating its home defence planning. This includes updating what is known as the government war book - a sweeping blueprint for the transition of the whole of society from peace to war.
This involves greater coordination between military and civilian authorities at a time of crisis.
"We will rigorously test these plans through the largest UK home defence exercise in several decades in 2027, to ensure that should the worst ever happen, we will always be ready," the minister said.
The announcements came after Sky News revealed more than two years ago that the UK did not have a national defence plan. The old Government War Book was shelved in the years that followed the end of the Cold War.
A major wargame podcast produced by Sky News last year exposed the limitation of the UK's ability to defend itself in the event of an armed attack by Russia.
Source: Sky News
--Agencies
