The civil defence network, mothballed since the Cold War ended, has been reactivated by a Home Office warning of a new threat - a wayward Chinese satellite that could crash into Britain at 1,000 mph in the next six weeks.
The threat from the satellite, which weighs a tonne but contains no nuclear material, is very real. The Ministry of Defence warned the Home Office last year that the faulty satellite, code-named FSW1, had gone into a decaying orbit 100 miles above the Earth.
The Chinese, who launched FSW1 in October 1993, have lost control of its guidance rockets, meaning that its eventual crash-landing site will be entirely a matter of chance and can only be calculated a few days beforehand.
It presently orbits the Earth once every 100 minutes, tracing a path between 56 degrees south and 56 degrees north - which includes all of Britain south of Glasgow and Edinburgh. The chances are, though, that it will end up in the ocean.
The Home Office contacted local authorities last October, and again in January, urging them to prepare "emergency planning measures" in case the satellite hit their locality.
"If it landed on your garden shed it would certainly demolish it," said Richard Tremayne-Smith of the British National Space Centre yesterday. "It does have some parachutes, but there is a lot of doubt about whether those will work.
"Even if the parachutes did operate, it would make a hell of a hole if it landed on your roof."
Any householder unlucky enough to receive this example of space technology could expect the repair bill to be paid by the Chinese government. Under an international treaty, countries that launch objects into space agree to pay for damage caused if or when they land.
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