Planned new laws to deal with a large-scale terror attack in Britain smack of "needless totalitarianism", said the Conservatives.
A terrorist attack on the UK is seen as a serious threat
Tory homeland defence spokesman Patrick Mercer was commenting on legislation which could allow the government to invoke a vast array of powers if Britain was attacked or was perceived to be at risk of a terrorist strike.
One Conservative peer on the cross-parliamentary committee looking at the Draft Civil Contingencies Bill suggested the plans could theoretically be used to turn Britain into a republic if a state of emergency was called.
The government says the measures are designed to ensure Britain has the best possible plans for dealing with an emergency, with clear responsibilities set out for those on the front line.
The measures would shake up legislation that dates back to the 1920s, giving ministers all the powers they need to tackle a wide range of incidents.
These would include allowing the government to rush through temporary legislation without prior parliamentary approval, and giving authorities the right to declare a regional state of emergency.
Mr Mercer told BBC News Online the draft laws contained "elements that smacked of needless totalitarianism".
But he added: "The reason we have a joint committee is to iron this sort of thing out.
"The last time we were threatened with something like this - either the danger of invasion by Hitler or the possibility of a nuclear bomb being dropped on us - we had to give the government enabling powers."
Current legislation was more suited for World War II, he said, and any new law had to strike a balance between being "effective and over-effective", he argued.
The comments came after
civil rights group Liberty warned that ministers would be left with almost limitless powers in the event of the legislation being invoked.
The organisation's Shami Chakrabati told the committee of MPs and peers that the draft legislation gave far too broad a definition of an emergency.
If the law were invoked, Parliament would later be recalled to discuss the issue, but Ms Chakrabati said the draft bill allowed for too great a delay in this.
Liberty was also concerned there would not be enough scrutiny of ministers' actions under the proposals.
One committee member, former Tory whip Lord Lucas of Crudwell, raised the prospect that "once a state of emergency is declared [the government] can effectively tear up the rest of the constitution and any bits of this bill [they do not like] and create a republic...".
Ms Chakrabati agreed that the most "colourful scenario" could see a secretary of state with "absolute legislative power" - theoretically mounting a threat to the whole UK constitution.
She added: "It is incredibly important that every safeguard possible is adopted in the legislation.
"Parliament needs to be convened immediately in a scenario like this and if something needs to be done before that, then fine, the executive acts."
Earlier this month a terror attack exercise was staged at one of London's busiest Tube stations.
The simulation, at Bank station, involved fire, ambulance, police and medical staff.
Teenage police cadets acted as passengers in a Tube train which was halted 50 yards short of the platform following "reports" of a chemical attack.
New equipment worth millions of pounds, including chemical suits, was tested in the exercise.
Five hundred emergency workers cordoned off streets, then rescued and decontaminated passengers, before taking them to hospital.