MI5's chief said "thousands of Islamist extremists in the UK;" What are the safeguards? How were they identified? Can they be deported?

Parker said "the most direct and immediate threats to the UK" are Al Quaeda and its affiliates in Pakistan and Yemen.

Will extremist elements in the UK and other western countries recognize ISIL as a leader, or remain apart from the "caliphate?"
I think they will ignore the "caliph."