EXERCISE ALBISTON SHADOW: INSIDE BRITAIN’S BIGGEST HOME DEFENCE EXERCISE IN DECADES
SPECIAL REPORT | NATIONAL SECURITY
Catch a Thief UK National Security News Special Report | 4 September 2026
UK prepares to test how government and the wider public sector would respond to hybrid attacks, while classified “War Books” are rewritten for the first time since 2004
Britain is preparing for what the Government describes as the largest UK home defence exercise in several decades, with ministers and hundreds of officials from across government and the public sector expected to participate.
Known officially as Exercise ALBISTON SHADOW, the multi-day exercise is scheduled for 2027 and will test government preparedness for hybrid attacks against the United Kingdom.
The precise scenario has been classified and the Government has not announced exactly when or where the exercise will take place.
The exercise is part of a much wider Home Defence Programme, under which the Government is also updating classified crisis plans traditionally known as the “War Books”.
The developments represent a significant change in the UK's approach to national resilience and home defence.
However, it is important to stress what ALBISTON SHADOW does and does not mean.
The exercise is preparation for a possible crisis or conflict; it is not evidence that the Government knows that a war is about to begin.
WHAT IS EXERCISE ALBISTON SHADOW?
On 14 July 2026, the Government announced that the UK's Home Defence Programme would deliver the country's largest home defence exercise in decades.
The official announcement stated that ministers and hundreds of officials from across government and the public sector are expected to participate.
The exercise will last several days and will test the Government's preparedness for hybrid attacks against the UK.
The Government has deliberately not disclosed the precise scenario.
This means that claims circulating online which describe a specific sequence of attacks, particular targets or a predetermined enemy scenario should not be treated as confirmed unless subsequently supported by official evidence.
The Government has confirmed only the broad nature of the exercise.
It is intended to test the UK's ability to respond to hostile activity below or alongside the threshold of conventional warfare.
Possible forms of hybrid activity discussed in media reporting include cyber attacks and sabotage, but these should be understood as examples of the type of threat being considered rather than a published ALBISTON SHADOW scenario.
The Government itself has not published the detailed scenario.
WHY IS BRITAIN DOING THIS?
The Government says the security environment has become increasingly complex, interconnected and contested.
The 2026 Resilience Action Plan implementation report says the UK has experienced, among other things, sub-threshold attacks attributed to Russia, major cyber attacks, new conflicts and increasingly severe weather during the previous year.
The Government's assessment is that modern threats increasingly blur the boundaries between domestic and international security, and between online and physical attacks.
A hostile campaign does not necessarily have to begin with conventional military forces crossing a border.
A combination of cyber attacks, disruption, sabotage, disinformation and attacks against infrastructure could create serious consequences for government, businesses and the public.
The Home Defence Programme is intended to strengthen the UK's ability to deter, respond to and recover from disruption caused by crisis and conflict, while bringing military and civilian planning closer together.
THE “WAR BOOKS” ARE BEING UPDATED
One of the most significant developments accompanying ALBISTON SHADOW is the Government's decision to update its classified War Books.
According to the Government, the plans were last updated in 2004.
The documents are coordinated by the Cabinet Office and are designed to help government departments plan how they would respond to threats against the UK.
The current programme is intended to update central crisis protocols and establish how departments would respond to conflict and threats against the UK mainland.
The updated documents are classified and the Government has not said that they will be made publicly available.
The House of Commons Library describes the renewed War Book work as part of a wider attempt to align military and civilian efforts during a period of crisis or international hostilities affecting the UK.
THE HISTORY OF THE WAR BOOK
The concept is considerably older than the Cold War.
The House of Commons Library records that a British Government War Book existed by 1912, when Prime Minister Herbert Asquith told Parliament that government departments had been given responsibilities for the outbreak of war.
The purpose was essentially to ensure that government machinery could move rapidly from peacetime administration to wartime arrangements.
After the Second World War, new War Books were developed.
During the Cold War, planning became heavily focused on the possibility of nuclear attack.
The Cold War War Book contained detailed instructions covering the actions ministers, officials and local authorities would be expected to take during escalating international tension and war.
The traditional War Book system was subsequently discontinued following the end of the Cold War.
The Government moved towards broader civil-contingency and emergency planning, with the Civil Contingencies Act 2004 becoming an important part of the modern framework.
The current Government's decision to revive the War Book concept therefore represents a return to a more explicit form of national conflict preparedness, although today's approach is intended to operate alongside the UK's broader all-hazards resilience system, rather than simply recreate Cold War civil-defence arrangements.
A TIMELINE OF BRITAIN'S RETURN TO HOME DEFENCE PLANNING
1912 War Book established
The House of Commons Library records that the Government had established a War Book by 1912 to coordinate departmental action if Britain entered a war.
Second World War and Cold War War planning expands
Following the Second World War, the Government developed new War Books. During the Cold War, the plans increasingly focused on the consequences of nuclear conflict.
1990s Traditional War Book system discontinued
Following the end of the Cold War and the reduction in perceived risk of major attack against mainland Britain, the traditional War Books were archived.
2004 Last reported update to the current War Book arrangements
The Government's July 2026 announcement states that the classified crisis plans commonly known as War Books were last updated in 2004.
2023 Government identifies the need for stronger domestic resilience
The 2023 Integrated Review Refresh and accompanying defence planning placed greater emphasis on identifying vulnerabilities and testing systems to protect the UK homeland during conflict.
August 2024 Home Defence Programme established
The Government established the Home Defence Programme in 2024.
Its purpose is to bring together defence, security and resilience planning and improve alignment between military and civilian efforts during international hostilities affecting the UK.
July 2025 Resilience Action Plan published
The Government published its Resilience Action Plan, establishing a strategic framework for improving UK resilience.
It adopted an “all hazards” approach, covering malicious and non-malicious risks and placing greater emphasis on whole-of-society resilience.
2025 COBR Directorate created
The 2026 implementation report states that the Government's COBR Directorate was formed in 2025 by bringing together the Resilience Directorate and the COBR Unit.
Its role is to support preparation, response and resilience against the most serious risks facing the UK.
2026 Home Defence planning accelerated
During 2026, the Government accelerated its Home Defence Programme and began updating the central crisis protocols traditionally known as War Books.
In May 2026, Armed Forces Minister Al Carns said the Cabinet Office was moving towards the new War Books by the end of the year so that government and local authorities would understand their roles during a crisis.
June 2026 Government warns of possible NATO conflict by 2030
The House of Commons Library records that then Prime Minister Keir Starmer warned in June 2026 that there could be a Russian attack on NATO “as soon as 2030”.
This is a risk assessment/warning, not a prediction that an attack will occur.
14 July 2026 ALBISTON SHADOW announced
The Government published its Annual Resilience Statement and the 2026 implementation report for the Resilience Action Plan.
It announced that the Home Defence Programme would deliver the largest UK home defence exercise in decades.
The exercise was named Exercise ALBISTON SHADOW.
It will be a multi-day exercise involving ministers and hundreds of officials from government and the public sector, testing preparedness for hybrid attacks against the UK.
The Government confirmed that the precise scenario would remain classified.
14 July 2026 National Risk Register updated
The Government simultaneously published an updated National Risk Register.
The Register is the public-facing version of the classified National Security Risk Assessment and is explicitly described by the Government as a planning tool rather than a prediction of future events.
Seven new risks were added.
These include risks associated with cyber attacks against data infrastructure, water infrastructure and police systems, as well as digital resilience failure.
The Government also added the risk of interference in the UK's democratic process.
The risk of disruption to Russian gas supplies was removed, reflecting reduced UK reliance on Russian gas.
Later in 2026 National resilience campaign planned
The Government says a national public awareness campaign will launch later in 2026.
It is intended to encourage households to take practical steps to improve resilience against risks including cyber attacks, flooding and severe weather.
The campaign will build on existing GOV.UK preparedness guidance and is also expected to include resources for schools and colleges.
2027 Exercise ALBISTON SHADOW
The major national exercise is scheduled to take place in 2027.
The exact date has not yet been publicly confirmed.
Indeed, on 28 August 2026, Conservative MP Ben Obese-Jecty submitted Parliamentary Question 23092, asking the Cabinet Office when in 2027 ALBISTON SHADOW would take place.
The parliamentary record currently shows the question as awaiting a response.
Therefore, as of the publication of this report, the precise date should not be reported as confirmed.
ALBISTON SHADOW AND NATO'S CMX27
ALBISTON SHADOW will complement NATO's forthcoming CMX27 exercise.
The UK Government says the two exercises will help ensure alignment between Britain, NATO allies and partners against a backdrop of rising threats.
The distinction is important.
ALBISTON SHADOW is focused on the UK's home defence and government preparedness, while CMX27 is a NATO-level crisis-management exercise.
The Government has not published the detailed scenarios for ALBISTON SHADOW.
WHAT DOES “HYBRID ATTACK” MEAN?
Hybrid threats can combine different forms of hostile activity rather than relying solely on conventional military force.
These may include:
- cyber attacks;
- disruption of critical infrastructure;
- sabotage;
- disinformation and influence activity;
- interference with democratic processes;
- attacks affecting communications or digital systems;
- hostile activity conducted below the threshold of conventional armed conflict.
It is important, however, not to confuse examples of hybrid threats with the actual classified scenario for ALBISTON SHADOW.
The Government has confirmed that the exercise will test preparedness for hybrid attacks, but it has not publicly disclosed the exact attack sequence or targets.
WHY CRITICAL INFRASTRUCTURE MATTERS
Modern Britain depends upon interconnected systems.
Electricity, water, telecommunications, transport, financial services, food distribution, healthcare and digital infrastructure all rely upon complex networks.
The Government's 2026 resilience documentation specifically highlights the interconnected nature of modern risks.
It also identifies supply-chain vulnerabilities and growing digital threats.
This creates a potential problem for national security planners: an attack on one system could have consequences for several others.
For example, a serious cyber incident affecting a critical service could create knock-on effects for businesses, emergency services and households.
The Government's resilience approach is therefore intended to involve not just the armed forces but government departments, local responders, industry, infrastructure operators, communities and the public.
THE PRIVATE SECTOR IS PART OF THE RESILIENCE PICTURE
The Government's 2026 Resilience Action Plan implementation report explicitly refers to working with utilities providers, businesses, civil society organisations, devolved and local government and Local Resilience Forums.
This reflects an important reality.
Much of the infrastructure upon which Britain depends is not directly operated by central government.
National resilience therefore cannot be achieved solely through the Ministry of Defence or Whitehall.
Businesses operating critical services and supply chains have an important role in maintaining continuity during severe disruption.
WHAT WILL ORDINARY MEMBERS OF THE PUBLIC SEE?
At present, there is no evidence that the Government intends ALBISTON SHADOW itself to involve the general public in a nationwide simulated attack.
The confirmed exercise involves ministers and hundreds of officials across government and the public sector.
The Government is, however, planning a separate national resilience campaign aimed at the public.
That campaign is expected to encourage households to prepare for emergencies and disruption, including scenarios involving severe weather and cyber attacks.
The Government says preparedness can help emergency services concentrate on people who are most vulnerable during a crisis.
WHAT WE DO NOT KNOW
Because the exercise scenario is classified, several important details remain unknown.
At the time of publication:
The exact date: Not publicly confirmed.
The exact locations: Not publicly disclosed.
The precise scenario: Classified.
The identity of the simulated attacker: Not publicly confirmed.
Specific infrastructure targets: Not publicly disclosed.
Whether members of the public will participate directly: No such nationwide public participation has been announced.
Whether the exercise will simulate an actual declaration of war: The Government says it will test preparedness for hybrid attacks; it has not published a scenario involving a specific declaration of war.
These distinctions are important because social media commentary has already gone beyond what has actually been confirmed.
IS ALBISTON SHADOW A SIGN THAT WAR IS IMMINENT?
There is no evidence that the exercise itself proves an imminent war.
Governments conduct exercises precisely because they cannot know with certainty which risks will materialise.
The Government's own National Risk Register explicitly states that it is a planning tool and not a prediction of future events.
At the same time, the scale of the exercise demonstrates that the Government considers the possibility of serious national disruption and conflict important enough to warrant a major, minister-led test of Britain's preparedness.
That is significant in its own right.
The Government is simultaneously:
- accelerating Home Defence planning;
- updating classified War Books;
- preparing a major national exercise;
- updating the National Risk Register;
- strengthening the role of civilian and local resilience structures;
- planning a national public preparedness campaign;
- and coordinating the exercise with NATO's CMX27.
Taken together, these measures show that homeland resilience and preparedness for conflict have moved considerably higher up the Government's agenda.
CATCH A THIEF UK SECURITY ANALYSIS
For security professionals, one of the most important aspects of ALBISTON SHADOW is arguably not the military dimension.
It is the recognition that national security increasingly depends upon civilian resilience.
A hostile actor does not necessarily need to defeat the British Armed Forces to cause serious disruption.
Disrupting communications, digital services, transport, utilities, supply chains or public confidence could create significant consequences without a conventional invasion.
That means national security increasingly intersects with areas traditionally considered civilian:
physical security, cybersecurity, CCTV, communications, access control, transport security, fuel supply, logistics, business continuity and community resilience.
For businesses, the lesson is straightforward: resilience cannot simply mean having a plan for a fire or flood.
Organisations increasingly need to consider what happens if the systems they depend upon communications, electricity, payment systems, internet connectivity, suppliers or transport become unavailable.
ALBISTON SHADOW is ultimately designed to test the Government's ability to cope with that type of interconnected crisis.
THE BOTTOM LINE
Exercise ALBISTON SHADOW is real.
It is scheduled for 2027.
It is officially described as the UK's largest home defence exercise in several decades.
It will involve ministers and hundreds of officials from across government and the public sector.
It will run for several days and test government preparedness for hybrid attacks against the UK.
Its detailed scenario remains classified.
It will complement NATO's CMX27 exercise.
At the same time, the Government is updating its classified War Books, which it says were last updated in 2004.
The Government is also strengthening wider national resilience planning and preparing a public awareness campaign for later in 2026.
The exact date of ALBISTON SHADOW has not yet been publicly confirmed.
What the exercise ultimately demonstrates is not that Britain expects war to begin in 2027.
Rather, it demonstrates that the British Government believes the country must be better prepared for a world in which conventional conflict, cyber warfare, sabotage, infrastructure disruption and other forms of hostile activity can overlap.
For the public and private sector alike, the message from Whitehall is increasingly clear:
National security is no longer regarded as solely the responsibility of the military. It is becoming a whole-of-government and whole-of-society responsibility.
SOURCES AND FACT-CHECKING
This report has been checked against primary and parliamentary sources, including the UK Government's 14 July 2026 announcement, the 2026 Resilience Action Plan Implementation Report, the House of Commons Library briefing on the War Book published 2 September 2026, and the Parliamentary record concerning the timing of ALBISTON SHADOW.
The Government's own documentation has been treated as the primary source wherever possible.
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