The protective marking system has been developed to protect sensitive information in Government. It is defined in the Cabinet Office Manual of Protective Security.
There are four main classifications, sometimes augmented by additional caveats and/or handling instructions:
The principle is that information is marked according to the harm that would result from its unauthorised disclosure and it is then protected by the appropriate marking to avoid this harm.
The Freedom of Information Act does not refer to the protective marking scheme because the fact that a document has a protective marking does not, in itself, mean that information cannot be disclosed.
A protective marking may indicate that an exemption is likely to apply and should at least be considered, but it is does not mean that the information is necessarily exempt from disclosure under the FOI Act. Conversely, although information that needs to be safeguarded for reasons of effective governance would normally be expected to bear a protective marking this may not always be the case.
When dealing with a request for information from a document that has a protective marking, it is always important to consider that the protective marking may no longer be current. The protective marking also reflects the highest classification of the information contained in a document: only a small amount of the content may warrant that classification. Wherever possible, reference should be made to the originator of the document in order to determine fully and accurately the present sensitivity of the information requested.