THE terror threat in Britain has been raised from "substantial" to "severe" in response to conflicts in Iraq and Syria, the Home Secretary Theresa May has announced.
'Severe' means that a terrorist attack is "highly likely", although Ms May stressed that there is no information to suggest an attack is imminent.
It is the fourth highest out of five levels of threat, with the highest being 'critical'. It was last changed in 2011, when it was reduced back down to substantial.
The decision to raise the terror threat comes amid increasing violence from Islamic State militants advancing across swathes of Syria and Iraq.
Speaking after the decision was announced, David Cameron warned Isis militants posed "a greater and deeper threat to our security than we have known before".
The Prime Minister said the West is "in the middle of a generational struggle against a poisonous and extremist ideology" that it could be fighting for decades.
"With Isis, we are facing a terrorist organisation not being hosted in a country, but actually seeking to establish and then violently expand its own terrorist state," he told a conference.
"We could be facing a terrorist state on the shores of the Mediterranean."