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Terrorism most immediate threat to UK, says MI6

Alex Younger said UK intelligence and security services had disrupted 12 terrorist plots since June 2013.

He said many of the threats came from ungoverned spaces in the Middle East - namely Iraq and Syria.

Mr Younger also warned that "hybrid warfare", which included cyber-attacks and subverting democracy, was becoming an "increasingly dangerous phenomenon".

"The risks at stake are profound and represent a fundamental threat to our sovereignty," he said. "They should be a concern to all those who share democratic values."