LONDON, Oct 3, 2008 (AFP) - The BBC planned to transmit reassuring messages in the event of a nuclear war, telling people to 'stay calm,' remain indoors, and conserve food and water, newly-released archives showed Friday.

The authoritative voice of the British broadcaster's Wartime Broadcasting Service would have transmitted a list of advice every two hours in the event of a nuclear attack by the Soviet Union during the Cold War.

'This country has been attacked with nuclear weapons. Communications have been severely disrupted, and the number of casualties and the extent of the damage are not yet known,' the message started.

'Remember, there is nothing to be gained by trying to get away. By leaving your homes you could be exposing yourselves to greater danger... Radioactive fall-out, which followed a nuclear explosion, is many times more dangerous if you are directly exposed to it in the open,' it added.

'Stay tuned to this wavelength, stay calm and stay in your own homes.

The transcript was part of files declassified by the National Archives, which releases official documents after 30 years.

The prospect of nuclear war between the two super-powers in Washington and Moscow was a real threat for decades during the Cold War, when public service films gave information about how to prepare in case of nuclear attack.

The archive files included recommendations that the BBC broadcast live updates, to underline that the BBC had not been 'obliterated,' and discussions over who should read the announcements to give them a more authoritative tone.

'The reassurance that 'the BBC is still there' would not be gleaned from a recorded announcement by an unfamiliar voice,' wrote Harold Greenwood from the Ministry of Posts and Telecommunications in a letter dated June 1974.

'Indeed, if an unfamiliar voice repeats the same announcement hour after hour for 12 hours listeners may begin to suspect that they are listening to a machine set to switch on every hour (or even that it has got stuck) and that perhaps after all the BBC has been obliterated,' he wrote.

The carefully-worded main announcement, to be repeated every two hours, included advice on how to conserve resources while inside after a nuclear strike.

'Stay in your own homes, and if you live in an area where a fall-out warning has been given stay in your fall-out room, until you are told it is safe to come out.

'The message that the immediate danger has passed will be given by the sirens and repeated on this wavelength. Make sure that the gas and all fuel supplies are turned off and that all fires are extinguished.

'Water must be rationed, and used only for essential drinking and cooking purposes. It must not be used for flushing lavatories. Ration your food supply: it may have to last for 14 days or more.

'We shall repeat this broadcast in two hours' time. Stay tuned to this wavelength, but switch your radios off now to save your batteries until we come on the air again.

'That is the end of this broadcast.'