The current threat level from international terrorism for the UK is assessed as SEVERE.
The threat level for Northern Ireland-related terrorism is set separately for Northern Ireland and Great Britain (England, Wales and Scotland). In Northern Ireland it is SEVERE and in Great Britain MODERATE.
SEVERE means that a terrorist attack is highly likely; MODERATE that an attack is possible, but unlikely.
For further information from MI5 on the history of the UK’s threat level, key points and business security advice please see here.