Sweeping new powers to tackle major terror attacks and other emergencies, have been proposed by ministers.
Security alerts are now a fact of life
The Civil Contingency Bill will update emergency laws dating back 80 years.
It could allow ministers to ban access to sensitive sites, evacuate affected areas and stop public gatherings without Parliament's approval.
Civil rights campaigners who were concerned about the breadth of the powers have welcomed moves to tighten the definition of "an emergency".
They had believed earlier draft plans gave ministers too much scope to effectively suspend Parliament.
MPs and peers on the parliamentary scrutiny committee set up to look at an earlier draft of the plans said they had "potentially dangerous flaws".
But the government says it has listened to those critics and has amended their plans accordingly.
The bill retains the government's right to amend any Act of Parliament to deal with an emergency, but accepts a recommendation by MPs that any special powers should lapse after 21 days, unless further approved by Parliament.
Change of heart
The special powers could include deploying the armed forces, requisitioning property or setting up a special court to deal with a disaster.
The government has responded to concerns about its definition of emergency by describing it in the bill as "an event or situation which threatens serious damage to human welfare, the environment or the security of the UK or a place in the UK".
Ban access to sensitive sites
Evacuate affected areas
Use the armed forces
Stop public gatherings
Set up special court to deal with disaster
Ministers agreed to ditch plans to include threats to "political, administrative or economic stability" of the country.
That was after a joint committee of MPs and peers said this would allow a future government to declare a national emergency just to protect its own existence.
Cabinet Office Minister Douglas Alexander told BBC Radio 4's the World at One programme: "We have listened to a very wide range of people on this matter.
"We have gone out to public consultation for 12 weeks. As a result we have tightened and strengthened the security people can feel in this country, but at the same time listened to their concerns about securing civil liberties.
"We believe the new definition of emergency in this bill addresses the concerns and strikes that balance."
'Work to do'
Shami Chakrabarti, director of the pressure group Liberty, welcomed the government's efforts.
"I do think the minister is right that what was originally a sweeping definition of public emergency has been tightened."
But she said there "may be some further work to do" on the bill.
Former minister Lewis Moonie, who chaired the joint committee which was critical of the draft plans, said the bill went a "very long way" to meeting those concerns.
Conservative shadow home secretary David Davis told BBC News 24: "There is no doubt this legislation is necessary.
"Indeed after two-and-half-years [since the 11 September attacks], I would think it was seriously overdue and it should have been rather better thought through by now."
Mr Davis said the powers were "not far from martial law" and worried the definitions of an emergency were still too widely defined.
Parliament also needed a say on whether ministers were using the powers correctly, he argued.
Liberal Democrat spokesman Tom Brake said the bill was now better but concerns remained.
He said more funding for emergency planning was needed and he complained about the "trust me" attitude adopted by the government.
Current emergency legislation is based on the 1920 Emergency Powers Act and the 1948 Civil Defence Act, which was drawn up to deal with the threat of an attack by the Soviet Union.
Although they already give police wide-ranging powers to take control of services and commandeer buildings and equipment, the new legislation is intended to ensure their actions are legally watertight in the event of circumstances not anticipated when the laws were drawn up.