The UK Threat Level is determined by the Joint Terrorism Analysis Committee (JTAC). This is an independent body, which sets the level based on security intelligence.  There are five  levels of threat (the highest being CRITICAL). Read more about the UK threat level. When the UK threat level moves to CRITICAL the NHS takes steps to prepare itself to respond to any imminent attack.

• Move to SEVERE 17 September 2017
• Move to CRITICAL 15 September 2017