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Classified information in the United Kingdom uses four levels of classification — from lowest to highest, they are: RESTRICTED, CONFIDENTIAL, SECRET and TOP SECRET. During the Second World War an additional level of TOP SECRET GUARD existed for extremely sensitive projects such as Ultra. Those working with such material must have the relevant security clearance and often must sign to confirm their understanding and acceptance of the Official Secrets Act. Government documents without a classification are tagged as "NOT PROTECTIVELY MARKED" (or NPM). Classified material must be accounted for in a manner appropriate to its classification level. Disposal must be in accordance with the Manual of Protective Security and the act of destruction or disposal is included in the accounting process.

Contents 1 Marking 2 Codewords 3 Security clearance 3.1 Counter-Terrorist Check (CTC) 3.2 Basic Check (BC) 3.3 Security Check (SC) 3.4 Developed Vetting (DV) 4 References 5 See also

All classified information must have a single-word description, taken from the following list:

• Appointments
• Budget
• Commercial
• Contracts
• Honours
• Investigation
• Management
• Medical
• Personal
• Policy
• Regulatory
• Staff
• Visits (domestic or foreign royalty and ministers)

One source also lists the following additional descriptors: Control, DS, Examination, Exercises, Intelligence, Locsen [see below], Operations, Police.

These markings may only be used when in conjunction with a protective marking, with the exception of personal, which can be used generally.

Protectively marked material may bear a caveat, which is a descriptor defining which nationality groups it may be shown to:

• UK EYES ALPHA — intended for the intelligence services, armed forces, and government. Must not be shown to any non-British citizen.
• UK EYES BRAVO — in addition to the ALPHA categories, also permitted to be shown to the Northern Ireland Office, List X companies, and member countries of the UKUSA Community liaising with the UK Joint Intelligence Committee.
• CANUKUS EYES ONLY — may only be shown to Canadian, UK or US citizens.[1]
• AUSCANNZUKUS — Australia, New Zealand, Canada, UK and USA. These countries comprise the UKUSA Community.

Documents with information about nuclear warheads, fusion, and naval nuclear propulsion must be classified CONFIDENTIAL or higher and include an "Atomic" label. There are further labels for atomic information: "Atomic Conifer" (material and general information on nuclear warheads), "Atomic Principal" (theory and internal design of nuclear warheads), and "Atomic Artificer" (details of the hardness of the Polaris and Trident missiles).

Other codewords include:

• ECLIPSE — may not be shown to Americans.
• LOCSEN — has local sensitivity, and may not be shown to local officials.
• NATSEN — has national sensitivity.
• DEDIP, DESDEN — may not be shown to certain named officials.
• DEYOU — regards corruption within the classified information system.
• NOFORN — no foreign dissemination.

Security clearance is checked at four levels depending on the classification of materials that can be accessed:

Required for personnel whose work involves close proximity to public figures, gives access to information or material vulnerable to terrorist attack or involves unrestricted access to certain government or commercial establishments. Does not allow access to any classified documents.

Not a formal security clearance. A basic check of the person's identity and employment/education referees, normally completed by the recruitment authorities or by certain defence industry companies. A pre-requisite for all other levels of clearance. Those with BC can view materials at RESTRICTED and possibly CONFIDENTIAL.

The most widely held clearance and allows uncontrolled access to material up to and including SECRET. This clearance also allows occasional and controlled access to TOP SECRET material. An SC involves a BC, plus checks against the UK criminal and security records (and if appropriate, of overseas countries) and a credit check. SCs are generally reviewed every ten years.

The highest level of clearance for those needing long-term and uncontrolled access to TOP SECRET information. This is the most comprehensive form of UK security vetting and is made up of the above BC and SC checks plus:

• The completion of a DV supplement questionnaire
• A financial check
• The checking of references in writing, by telephone or by interview from personal friends, tutors and employers as appropriate
• A detailed interview with the person needing the clearance conducted by a vetting officer.

• UK-USA Classification Equivalency Table, Los Alamos National Laboratory

• Classified information
• Classified information in the United States