Britain is massively unprepared for a catastrophic terrorist attack, a series of confidential Downing Street documents seen by The Independent on Sunday reveals.

The documents disclose that the nation's civil defence "effectively no longer exists", that the emergency services have "not attempted" to become fully prepared for the threat, and that legislation is so "anachronistic and ineffective" that the Government could not even declare a state of emergency.

The disclosures – much the most devastating official admission yet of Britain's vulnerability – closely follow last week's government announcement that it would stockpile enough smallpox vaccine to be able to vaccinate everyone in the country if necessary.

They come amid increased concern that al-Qa'ida is about to mount an attack on Britain, and as the crisis over Iraq reaches a new intensity with yesterday's delivery of its dossier on weapons of mass destruction to the UN. Many experts agree that war with Iraq would be greatly increase the possibility of chemical, biological and nuclear weapons being used in London and other cities.

The documents – compiled between September and 5 December by the Civil Contingencies Secretariat based in the Cabinet Office – warn of "catastrophic incidents... simultaneously occurring in diverse locations, arising from terrorist attack". It says that the "devastating" use of weapons of mass destruction threatens "the viability of the nation as a whole". But they add that while Britain can "respond effectively to smaller-scale emergencies", the capacity to deal with big ones still "is urgently required" 15 months after the 11 September attacks. Recent floods and the foot and mouth and fuel price crises – though less disruptive than a major terrorist attack – had exposed "poor communication between central and local government", "a lack of clarity over roles and responsibilities", and "inconsistencies in roles and arrangements".

They describe how after the end of the Cold War "most civil defence infrastructure and initiatives were scrapped or suspended", and conclude: "Civil defence effectively no longer exists in the UK as a stand-alone practical activity."

Meanwhile, they add, Britain's emergency legislation is "out of date". They say that "though useful and common internationally", the "ability to declare a state of emergency effectively does not exist in the UK" because the 80-year-old law under which it would be done is "anachronistic".

Local councils, they say, give emergency planning a low priority because they are not bound by law to ensure it is carried out, and because "they appear to be distracted by the multifarious range of important functions for which they are responsible". As a result, some local authorities had not prepared proper plans for dealing with a possible terrorist attack.

Police, fire and ambulance services, for their part, had gone at "only a slow pace" in modernising their responses, and had "not attempted" to meet the full agenda for change laid out by the Government.

The documents say that new legislation is urgently needed to "ensure civil protection" and that, without it, the lack of preparation will get even worse. But ministers are dragging their feet.

They failed to include a new Civil Contingencies Bill in the Government's legislative programme, announced in last month's Queen's Speech, and do not even plan to publish a draft of it until the spring.

Senior Cabinet Office sources told The Independent on Sunday last week that they were frustrated by the contrast between the alacrity of ministers in clamping down on civil liberties after 11 September and their reluctance to take adequate measures to protect the public from attack.