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14 August 2023 - We have included the following new Further Reading resource:

  • Keeping internal consultations on FOI requests timely and transparent - a short guide for public authorities

About this detailed guidance

This guidance discusses section 26, the defence exemption of FOIA, in detail and is written for use by public authorities. Read it if you have questions not answered in the Guide, or if you need a deeper understanding to help you apply this exemption in practice.

In detail

What exemptions are contained in section 26 of FOIA?

Section 26(1)(a) provides an exemption for information if its disclosure would, or would be likely to, prejudice the defence of the British Islands or of any colony.

Section 26(1)(b) provides an exemption for information if its disclosure would, or would be likely to, prejudice the capability of, effectiveness or security of any relevant forces.

Section 26(3) provides an exemption from the duty to confirm or deny whether information is held if doing so would, or would be likely to, prejudice any of the matters mentioned in subsection 26(1).

All the exemptions are subject to the public interest test. 

How should we interpret the terms used in the exemptions?

Section 26(2) explains that “relevant forces” means the armed forces of the Crown and any forces co-operating with those forces or any part of them.

“Armed forces” is not defined in FOIA but will include any member or part of the regular and reserve naval, land and air forces of the UK. However, special forces are not armed forces for the purposes of FOIA. Information obtained from them, or related to them, is subject to the absolute exemption at section 23 (security bodies) of FOIA.

Forces co-operating with the UK’s armed forces would include foreign armed forces committed to collective defence arrangements, for example NATO or UN troops. It would also include forces co-operating in more informal alliances, for example the forces of the Northern Alliance before the fall of the Taliban regime in Afghanistan.

 “British Islands” is defined in Schedule 1 of the Interpretation Act 1978 as meaning the United Kingdom, the Channel Islands and the Isle of Man.

“Colony” is defined in the same legislation as meaning any part of Her Majesty’s dominions outside the British Islands except for a Commonwealth country, a territory whose external relations is the responsibility of a country other than the UK, and any associated state.

How should we apply the exemptions in section 26(1)?

Section 26(1) is a prejudice based exemption which states that information is exempt if its disclosure would, or would be likely to, prejudice:

“(a) the defence of the British Islands or of any colony, or

(b) the capability, effectiveness or security of any relevant forces.”

Prejudice to defence

The need to maintain the defence of the British Islands and colonies is not restricted to a period of military activity. However, there is likely to be a difference between what is required for the defence of the nation in peacetime, during a preparation for war, and during actual hostilities.

You should therefore consider what the defence of the nation may reasonably require at the time of the request before deciding whether the exemption applies.

The defence of the nation is not limited to activities within the British territories. The exemption may also apply to activities overseas to prevent attacks being launched against the British territories, for example activities abroad aimed at combating international terrorism.

You should not assume that the information covered by the exemption will only be held by the Ministry of Defence (MOD) or the armed forces. For example, fire authorities and those involved in emergency planning may also hold information that may be caught by the exemption.


Armed forces are sometimes deployed to provide an emergency fire service during a firefighters’ strike. Information about the deployment and number of troops involved could be exempt under section 26 if its disclosure would be capable of assisting an enemy or potential enemy. 

Prejudice to the capability, effectiveness or security

Prejudice to the capability, effectiveness or security of relevant forces means anything that could put the physical safety of such forces at risk or affect their ability to carry out their duties.

The following list, though not exhaustive, gives some examples of information that may prejudice the capability, effectiveness or security of the armed forces if disclosed:

  • Policy and strategy, planning and intelligence.
  • Operational orders, tactics and rules of engagement.
  • General capability and effectiveness, for example the performance of troops or military equipment and weaponry.
  • Plans and measures covering:
    • the maintenance of essential supplies and services needed for military operations;
    • military capabilities, current and future, including access to and availability of weaponry;
    • defence or reinforcement of other countries including any formal or informal arrangements and agreements; and
  • less clearly related information such as details of fuel and other important supplies, and the location of telecommunications equipment and military transport.

The prejudice test

You can only withhold information on the basis of section 26(1) if its disclosure would, or would be likely to, prejudice one of the activities listed in the subsections of the exemption.

The test involves several steps:

  • Whether the harm is one that the exemptions in section 26(1) are designed to protect.
  • Whether you can demonstrate a causal link between the disclosure and the harm. The prejudice must be real, actual or of substance. However, you do not necessarily have to demonstrate quantifiable loss or damage.
  • The likelihood of the harm actually occurring (ie “would” it occur, or is it only “likely to” occur?).

Deciding whether the prejudice would occur or is only likely to occur is important. The more certain the prejudice, the greater weight it will carry when considering the public interest. In this context the term “would prejudice” means that it has to be more probable than not that the prejudice would occur. “Would be likely to prejudice” is a lower test; there must be a real and significant risk, even if the risk of prejudice occurring is less than 50 per cent.

Read our detailed explanation of the prejudice test in our guidance on the prejudice test.

Key factors affecting prejudice

You should consider the following in deciding whether disclosure of information would be prejudicial:

  • The timing of the request. Information which might prejudice the effectiveness of a military operation that was planned or underway might cause no harm once the operation had been concluded. However, there will also be cases where the disclosure of information about the tactics or weaponry involved in a successful operation might prejudice the chances of success in a similar operation in the future.
  • The age of the information. The disclosure of information several decades old could still be prejudicial if it revealed operating techniques and tactics still used today.
  • What information is already in the public domain. If the same information is available from other, reliable sources, it will rarely be possible to argue that repeated disclosure would cause prejudice. By contrast, if the information available from elsewhere is more speculative (even though, in fact, true), then it will be easier to argue that disclosure would be prejudicial. Similarly, you may legitimately decide to withhold information that itself is relatively innocuous if that information would cause prejudice in combination with another piece of information that is already in the public domain.


In the request considered in decision notice FS50838374 the complainant asked the MOD for a copy of the second edition of a document entitled “JSP900: UK Targeting Policy”. The MOD provided a redacted version of the document but argued that the remaining parts of it were exempt from disclosure under FOIA on the basis of section 26(1)(b), as well as several other exemptions.

In support of its reliance on section 26(1)(b) the MOD argued that, as the name of the requested document suggested, it contained the

targeting policy the UK adopts at every stage of a military operation. The MOD noted that this was an older edition of the document but the operational tactics and capability performance it contained were still current. So the MOD argued that its disclosure would give hostile nations and enemy combatants an insight into the armed forces’ decision making process, enabling them to change their tactics, techniques and procedures (TTP). The MOD argued that this would increase the risk to UK forces. The MOD also argued that the level of prejudice was set at the higher threshold of “would” prejudice.

The Commissioner accepted that the type of harm that the MOD believed would occur if the information was disclosed applied to the interests protected by section 26(1)(b) of FOIA. The Commissioner was satisfied that disclosure of this information clearly had the potential to harm the capability and effectiveness of UK forces in operations, given that it detailed the TTPs used by UK forces and also outlined their targeting capabilities. Furthermore, taking into account the MOD’s arguments and the content of the withheld information, the Commissioner was satisfied there was a real and significant risk of this prejudice occurring as the information would directly assist enemy forces in building up a picture of the targeting practices. They also agreed with the MOD that the higher threshold of “would prejudice” was met.

How should we apply the ‘neither confirm nor deny’ provisions?

Section 26(3) says:

“The duty to confirm or deny does not arise if, or to the extent that, compliance with section 1(1)(a) would, or would be likely to, prejudice any of the matters mentioned in subsection (1).”

If you are relying on section 26(3), you must be able to explain how confirming or denying that information of a given description is held could pose a risk to defence matters or the capability, effectiveness or security of the armed forces.


The case of Donnie Mackenzie v Information Commissioner, EA/2013/0251 (7 July 2014) concerned a request for a list of directed energy weapons such as radio frequency, laser and acoustic and other non-lethal weapons that the MOD had access to. The MOD relied on section 26(3) of FOIA to refuse to confirm or deny whether it held the requested information. The Commissioner issued a decision notice upholding the MOD’s position.

The First-tier Tribunal (FTT) also upheld the MOD’s reliance on section 26(3), concluding that “details of any UK capability in this area would be of considerable interest to any hostile power and would assist that power in devising counter-measures or give it reassurance that no counter measures were necessary. It would remove uncertainty and assist in the planning or execution of any hostile action. This would therefore prejudice the capability effectiveness and security of British forces.”

Read our detailed explanation of the ‘neither confirm nor deny’ provisions in this guidance.

How do we consider the balance of the public interest test?

Section 26 is a qualified exemption. This means that even if the requested information is exempt from disclosure, you must consider whether the public interest in maintaining the exemption outweighs the public interest in its disclosure.

Arguments in favour of disclosure

FOIA does not list the factors that would favour disclosure. However, they may include:

  • furthering the understanding of, and participation in the public debate of issues of the day;
  • promoting accountability and transparency in how public money is spent;
  • helping individuals understand decisions made by public authorities which affect their lives;
  • informing the public about measures, procedures, arrangements and associated discussions concerning public protection; and
  • bringing to light information affecting public health and safety.

More specifically, in the context of section 26 you should consider whether any of the following points are relevant:

  • The public may have more confidence in the government of the day, and be more supportive of key decisions, if they understand the rationale behind whether to deploy troops or go to war.
  • The public have a natural concern about the effectiveness of the armed forces, and any risks to the safety of military personnel and civilians.
  • Military action can result in loss of life. Disclosure of subsequent discussions about the safety of equipment or direction of the operation could support improvements to equipment or planning, and allow individuals to challenge the basis of decisions affecting them personally.

Arguments in favour of maintaining the exemption

Factors that will carry significant weight in favour of maintaining the exemption are those where disclosure of information:

  • would or would be likely to compromise a specific military operation;
  • may adversely affect the security or safety of military personnel or civilians, for example by revealing weapons transport routes; and
  • may reveal information received from an ally. That country may object to disclosure or consider it a breach of confidentiality. This could prejudice defence relations by restricting future exchanges of information or by jeopardising military co-operation.

Balancing the public interest test

There is a clear public interest in the defence of the country and in ensuring that the effectiveness of the armed forces is not undermined. However, the exemption is not an absolute one.

You must consider the relative weight of the arguments for and against disclosure given the circumstances of the particular request. These can be affected by the likelihood and severity of any prejudice, the age of the information, how far the requested information will help public understanding and whether similar information is already in the public domain.


The case of Chris Cole v the Information Commissioner and Ministry of Defence, EA/2013/0042 & 43 (30 October 2013) involved two requests concerning the operational use of the UK’s Unmanned Aerial Vehicles (UAVs) in Afghanistan.

The MOD disclosed some information falling within the scope of the requests but withheld the rest under section 26(1)(b) of FOIA. It also claimed that certain information was exempt under section 27 (international relations).

The Commissioner agreed with the MOD that section 26(1)(b) applied and that the public interest favoured maintaining the exemption.

The Tribunal upheld that conclusion on appeal. Regarding the public interest test, it stated that, “The public interest in maintaining the exemption in section 26(1)(b) is exceptionally weighty. There is an exceptionally strong public interest in preventing harm to the UK’s capabilities in an ongoing armed conflict. The security and safety implications carry very strong public interest weight. We agree with the Commissioner that there would need to be very weighty countervailing considerations to outweigh a risk to security and safety of the forces which was of sufficient severity to have engaged section 26(1)(b).”

The Tribunal acknowledged that there were “legal and ethical implications in the use of armed UAVs and we agree that these implications should be considered as part of an informed public debate. There is significant public interest in transparency about the UK’s use of armed UAVs”. However, the Tribunal was not persuaded that the information that was the subject of the appeal would inform this debate.  

In contrast, the Tribunal emphasised that it was satisfied that disclosure of the information “would cause real risk to life of troops in Afghanistan, both now and in the future” and that “this is an active campaign with a real, identified enemy whose capabilities are unknown but are adapting”. It therefore concluded that the public interest in maintaining the exemption far outweighed any public interest in disclosing the information.

Further reading 

Other exemptions may be relevant to section 26 and you may want to read our guidance on them: