A number of Britons are feared dead following the terror atrocities in Paris, David Cameron has said.
The Prime Minister condemned the "brutal and callous murderers" behind the series of attacks in the French capital.
"We must be prepared for a number of British casualties," he warned.
Speaking in Downing Street he said the terror threat level in the UK would remain at "severe", but the attack would prompt a review of plans and suggested the threat posed by Islamic State was "evolving".
In a message of solidarity to the people of France he said: "Your values are our values, your pain is our pain, your fight is our fight."