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Threat levels are designed to give a broad indication of the likelihood of a terrorist attack. They are based on the assessment of a range of factors including current intelligence, recent events and what is known about terrorist intentions and capabilities. This information may well be incomplete and decisions about the appropriate security response are made with this in mind.
Together with the detailed assessments behind them, this analysis informs security practitioners in key sectors and the police of the potential threat of terrorist attack. Threat assessments are also produced as necessary for individuals and events. There are five threat levels which inform decisions about the levels of security needed to protect our Critical National Infrastructure (CNI).