The United Kingdom does not disclose details of its system of alerts.
Officially, it says the country is on a heightened state of alert. But British media say the terrorist threat level was secretly lowered on August 18 to "severe general", the third highest rating in a seven-tier system.
Threat and alert levels identified by media are:
1 - Critical (precise intelligence of a planned attack with timing and location known)
2 - Severe specific (intelligence warning of a known terrorist plot)
3 - Severe general (a high possibility of attack at some stage but without knowledge of the timing or target)
4 - Substantial (still a high alert but no intelligence of a specific plot)
5 - Moderate
6 - Low
7 - Negligible.