MI5 to send out terror alerts via email

Subscribers entering their email address will receive a message with the words ''MI5 news update'' whenever there is a change on the website.

This could include a warning that the threat of an attack is higher or lower, though given the number of alleged plots under investigation, the level is unlikely to fall for many years.

The current level, as assessed by the Joint Terrorism Analysis Centre based at MI5's London headquarters, is severe. This is the second highest point on the five-grade system and means that an attack is highly likely but there is no specific information.