Chat with us in Facebook Messenger. Find out what's happening in the world as it unfolds.

Caption:LONDON, ENGLAND - AUGUST 29: A police officer stands in Downing Street on August 29, 2014 in London, England. British Home Secretary Theresa May announced today that the UK's terror threat level is being raised from 'substantial' to 'severe' in response to the current conflicts in Iraq and Syria. (Photo by Dan Kitwood/Getty Images)
Caption:LONDON, ENGLAND - AUGUST 29: A police officer stands in Downing Street on August 29, 2014 in London, England. British Home Secretary Theresa May announced today that the UK's terror threat level is being raised from 'substantial' to 'severe' in response to the current conflicts in Iraq and Syria. (Photo by Dan Kitwood/Getty Images)

    JUST WATCHED

    Terror plot foiled in the UK?

MUST WATCH

Terror plot foiled in the UK?

United Kingdom police arrest 4 men suspected of terror plot. CNN's Nic Robertson reports.

Terror plot foiled in the UK?

United Kingdom police arrest 4 men suspected of terror plot. CNN's Nic Robertson reports.