The full gamut of dangers facing Britain, from terrorist plots to disasters caused by climate change, is to be spelt out by the Government in the form of an annual national threat register, Gordon Brown announced.

A new-style civil defence network, modelled on the Second World War air-raid wardens – “but without the uniforms” – is also to be set up. Members of the public can join it to help local authorities and emergency services at a time of national crisis.

As he announced a national security strategy, the Prime Minister made it clear that he wanted the public to be more involved and better informed about the threats facing this country over the next ten to twenty years.

The idea of a national threat register was not to alarm people but to put into the public domain what was currently “highly classified” information, Margaret Aldred, a senior official in the Cabinet Office, said yesterday.

The register, to be published this year, might even spell out the expected casualty toll of a major incident. Last year the Government carried out the largest-ever emergency exercise, Operation Winter Willow, which was based on Britain being hit by a flu pandemic that killed 750,000 people.

Mr Brown said the publication of the national security strategy, written by the Cabinet Office, was the first time that a government had drawn together into one document all the perceived threats and the structures put in place to deal with them.

Robert Hannigan, the Prime Minister’s intelligence and security adviser, confirmed that as part of the attempts to be more open about security threats, the heads of MI6, MI5 and GCHQ would soon be required to give evidence in public to MPs, as exclusively reported in The Times yesterday. They will appear before the parliamentary Intelligence and Security Committee (ISC).

The Cabinet Office document also confirmed that Mr Brown wants an independent national security forum, made up of about 30 experts, to act as an advisory body.

However, Mr Brown has rejected the idea of copying the United States and forming a homeland security department. Last year he established a new Cabinet committee, the National Security, International Relations and Development Committee (NSID) which, officials said, he felt had the right broad-based authority to make decisions across Government.

The Cabinet Office White Paper emphasised that the overarching aim of the security strategy was to enable “people to go about their daily lives freely and with confidence”, and with a “reasonable assurance of safety”.

Although there was currently “a very low risk” of military attack on Britain, the “security landscape” was becoming increasingly complex.

Included in the threats delineated in the White Paper was cyber warfare. Mr Hannigan revealed that Britain had been subjected to cyber attacks from a number of countries. Last year it was disclosed that attacks on government computer systems were believed to have emanated from China. Russia is also believed to have tried to penetrate government networks.

The White Paper said that terrorists were not interested just in causing mass casualties “without warning”, but also aspired to target Britain’s national infrastructure using new methods, including electronic attacks.

Mr Brown said that staffing levels at MI5 would rise to 4,000 – double what it was in 2001 – and funding for the Joint Terrorism Analysis Centre, which is run by MI5, is to increase by 10 per cent. He also referred to four new regional counter-terrorist units and a 1,000-strong civilian force that would act as a standby body to go anywhere in the world.

However, there are three regional counter-terrorist units already operating. A standby force of civilian experts, consisting of former judges and ex-police and army officers, also exists, and will be 1,000-strong by June.

Potentially the greatest challenge to global security, the White Paper said, would come from climate change. “Many of these changes will affect the United Kingdom, but the direct effects are likely to fall most heavily on those countries least able to deal with them, and therefore most likely to suffer humanitarian disaster, but also to tip into instability, state failure or conflict.”

Officials confirmed that the national security strategy proposals would have to be paid for out of existing budgets; however, the White Paper admitted that the Ministry of Defence was facing “acute cost pressures”, mainly because of the rise in equipment costs.

David Cameron agreed that there was a need for a national security strategy but dismissed the idea of a national security forum as “a talking shop”.

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