What are the MOD's security classifications?

In April 2014, the system was simplified into three levels: OFFICIAL, SECRET, and TOP SECRET.

The Ministry of Defence (MOD) works to the UK Government's security classifications.

Security classifications indicate the sensitivity of information – in terms of the likely impact resulting from compromise, loss or misuse – and the appropriate level of protection that it needs. 

Historically, a six-tier system was used: UNCLASSIFIED, PROTECT, RESTRICTED, CONFIDENTIAL, SECRET, and TOP SECRET.

This was revised by the Government Security Classifications Policy, which was brought in in 2014 to make it easier to correctly classify information and ensure all parts of Government worked to a single framework.

That meant the system was simplified into just three levels: OFFICIAL, SECRET, and TOP SECRET.

These are defined as:


This includes routine business operations and services, some of which could have damaging consequences if lost, stolen or published in the media, but are not subject to a heightened threat profile.


Very sensitive information that justifies heightened protective measures to defend against determined and highly capable threat actors.

For example, where compromise could seriously damage military capabilities, international relations or the investigation of serious organised crime.

Top Secret

The Government's most sensitive information requiring the highest levels of protection from the most serious threats.

For example, where compromise could cause widespread loss of life or else threaten the security or economic wellbeing of the country or friendly nations.

In addition, although not an official classification, OFFICIAL SENSITIVE refers to information that falls under the OFFICIAL classification but requires additional special handling.

The MOD defines information as sensitive if "in the wrong hands, it could potentially put at risk someone's safety, or result in harm to the work of defence or of the Government more widely."

Unlike in most other Government departments, MOD policy is that official information should not be routinely marked unless it is sensitive – in which case it should be marked OFFICIAL SENSITIVE

According to the MOD, 80% of the department's information falls into the OFFICIAL category and is therefore not to be marked.

Meanwhile, an investigation into how secret MOD papers ended up at a Kent bus stop in June 2021 has found no evidence of espionage, but instead blamed an individual's blunder.

Cover image: Half-shredded "Top Secret" classified Government correspondence (Picture: Stephen Barnes/Law and Order/Alamy Stock Photo).