Section 31: National security and defence

When withholding is required to safeguard national security, or disclosure would substantially prejudice the defence of the British Islands.

National security and defence#

Section 31 of FOISA exempts information where withholding is needed to safeguard national security, or where disclosure would substantially prejudice defence capabilities.

In plain terms#

The authority is saying: releasing this information would put national security at risk or damage the country’s ability to defend itself. In practice, Scottish public authorities rarely hold the kind of information this exemption covers - most national security and defence material sits with UK-level bodies under the UK FOI Act.

You ask a Scottish university for records about a research partnership with the Ministry of Defence. The university refuses some material under section 31, arguing that revealing technical details would substantially prejudice the effectiveness of the armed forces.

The legal detail#

Section 31(1) exempts information where exemption is “required for the purpose of safeguarding national security.” There’s no prejudice test here - the question is simply whether withholding is required for national security.

Section 31(4) exempts information where disclosure would, or would be likely to, substantially prejudice the defence of the British Islands or the capability, effectiveness, or security of the armed forces (or any forces co-operating with them).

A member of the Scottish Government can sign a certificate under section 31(2) stating that the exemption is required for national security. That certificate is treated as conclusive evidence - meaning, on its face, it settles the matter. However, the certificate can be challenged before the courts.

Absolute or qualified?#

Both limbs are qualified. The public interest test applies. Even where the authority (or a minister) claims national security or defence concerns, the Commissioner can consider whether the public interest in disclosure outweighs the interest in withholding.

There is, however, a significant qualification. The First Minister has the power under section 52 of FOISA to overrule the Commissioner on section 31(1) decisions by issuing an executive override certificate. This power has never been used.

See What can they refuse? for more on how the public interest test works.

How it’s used in practice#

Section 31 is uncommon in Scottish FOI. Defence and national security policy are reserved to Westminster, so the UK Government and its agencies hold most of this material. Where it does arise in Scotland, it tends to involve Police Scotland (counter-terrorism), the Scottish Government (in dealings with UK security bodies), or public bodies with links to defence research.

The ministerial certificate mechanism is distinctive. Under section 31(2), a Scottish Government minister can issue a certificate that effectively overrides the Commissioner’s judgement on whether the exemption applies. No other exemption works quite like this. The certificate can be challenged by judicial review in the Court of Session, but the burden on the requester is heavy.

Where authorities rely on section 31(4) - the defence limb - they must meet the substantial prejudice test. Vague claims about security risks aren’t enough. The authority should explain how disclosure of the specific information would cause real and significant harm to defence capabilities.

How to challenge it#

Ask whether the authority has explained which limb of section 31 it’s relying on. Section 31(1) and section 31(4) have different tests, and the refusal should make clear which applies.

If the authority relies on section 31(4), check whether it has identified the specific prejudice. A blanket claim that the information is “security-sensitive” doesn’t meet the substantial prejudice threshold.

Consider whether the information is already in the public domain. Defence-related information that has been published elsewhere, reported in the media, or disclosed under the UK FOI Act may no longer need protection under section 31.

See What to do if refused for the full process.

You can also use our interactive challenge tool for this exemption to work through these questions step by step and draft a review request.

Good to know: There is no time limit on sections 31(1) or 31(4) - both can apply to records of any age. The authority can also neither confirm nor deny whether it holds the information, but only if the information (if held) would be exempt under section 31 and revealing whether it exists would be contrary to the public interest (section 18).