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."
Islamist militants have reinforced the siege against 40 Filipino peacekeepers trapped in Syria's Golan Heights, according to diplomatic sources at the United Nations.
More than 20 vehicles carrying armed fighters were seen approaching the region which has been demilitarized and monitored by the United Nations Disengagement Observer Force since Israel and Syria signed an armistice in 1974.
Earlier, nearly three dozen peacekeepers who were trapped by militants in the Golan Heights were successfully extracted, according to UN officials.
Nearly three dozen United Nations peacekeepers who were trapped by militants in the Golan Heights have been successfully extracted, according to UN officials.
Officials in the Philippines have said all 72 of the trapped Filipino peacekeepers were safe.
Another 44 Fijian peacekeepers have been detained by militants nearby since Thursday.
Michael Foley fondly recalls his "selfless" brother James and urges more support for independent journalists recording from conflict zones.Read the full story ›
The brother of murdered journalist James Foley has urged the US Government and its allies to do more to secure the safety of fellow American journalist and Islamic State hostage Steven Sotloff.
Speaking to Good Morning Britain, Michael Foley said, "I don't have all the answers but what I can say is that I urge the US Government, our partners and our allies to do everything they can and to treat this with the utmost sense of urgency because there [are] things that can be done."
"Certainly we don't have complete control over the situation, but I just want to make sure for Stephen's family and for others that we are doing everything possible."
At least four hostages held in Syria by Islamic State militants, including US journalist James Foley, were waterboarded during their captivity, The Washington Post has reported.
The newspaper, citing people familiar with the treatment of Western hostages, said the Islamic State captors appeared to model the technique used by the CIA on three terrorism suspects captured after the 11 September attacks on the World Trade Center.
A source close to the family of a hostage held by Islamic State acknowledged to Reuters that hostages had been waterboarded, but gave no further details.
Waterboarding, a process characterised by Barack Obama and many other US politicians as torture, simulates drowning. Captives have water poured over their noses and mouths until they feel as if they are suffocating.
Three Americans and fewer than 10 other western hostages are still being held by the militant group, according to people familiar with the situation.
More than 150 Syrian soldiers were stripped and marched into the desert to be shot by Islamic State militants, activists have claimed.
A video has been posted to YouTube purporting to show the men, who are barefoot and in their underwear, being escorted into the desert.
It then goes black before revealing a similar number of men, also in their underwear, lying dead in the sand.
The video has yet to be verified but correspond to other reports from the region, and tie up with a statement and claims made via Twitter relating to the mass killing of troops captured in recent fighting for a string of military bases in north-eastern Syria.
There has been no immediate comment from the Syrian government.
The UN is "making every effort to secure the release" of 43 peacekeepers detained by an armed group near Al Quneitra in the Golan Heights.
A further 81 peacekeepers are "currently being restricted to their positions" near Ar Ruwayhinah and Burayqah, the UN said.
The nationalities of the peacekeepers, who were serving with the UN Disengagement Observer Force Zone (UNDOF), is not clear. As of 31st July, there were peacekeepers from Ireland, the Netherlands, Fiji, Nepal, India and the Philippines serving in the force.
Syrian jets shelled rebel positions near the Quneitra border crossing between Syria and the Israeli-occupied Golan Heights and fighting in the area is ongoing.
The United Nations has said that 43 of its peacekeepers in the Golan Heights have been detained today by an armed group in Syria.
It is working to secure their release.
A spokesman for UN Secretary-General Ban Ki-Moon has said that any violation of the ceasefire agreed today would be "utterly irresponsible".
He said the blockade of Gaza must end, and that the territory must be brought back under the control of one legitimate Palestinian government adhering to Palestine Liberation Organisation commitments.
"Israel's legitimate security concerns must be addressed," he added.