<P> The United Kingdom Terror Threat Levels, often referred to as UK Threat Levels, are the alert states that have been in use since 1 August 2006 by the British government to warn of forms of terrorist activity . Before then a colour - based alert scheme known as BIKINI state was used . The response indicates how government departments and agencies and their staffs should react to each threat level . </P> <P> The current level was reduced to Severe on the afternoon of 17 September 2017 / It had been raised to Critical following the 2017 Parsons Green bombing on 15 September . </P> <P> The previous threat level to that was Severe having been reduced to that level following an increase to Critical after the Manchester Arena bombing of 22 May 2017 . </P>

What level of terror alert is the uk at