Politicians should not act as "cheerleaders" for the intelligence and security services, according to former Liberal Democrat leader Lord Ashdown.
Writing in The Observer newspaper he said the Conservative Party had used the decision to raise the terror threat level "to tell us how frightened we should be and why this required a range of new powers for them to exercise".
He added that the new range of executive powers "could endanger our liberties."
He said: "Of course, in these circumstances, the police and the security services will lead the clamour for more powers. They are charged by us to maintain our safety."
He added: "But it is the job of politicians to act, not as cheerleaders for those demands, but as jealous protectors of our liberties who measure any demand for their reduction against necessity, supported by evidence."