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The world’s worst ever nuclear accident, at Chernobyl in 1986, sent a plume of highly radioactive material into the atmosphere first detected outside the immediate region by atomic workers in Sweden.
Contamination arrived in Britain through light nuclear rain, and radiocaesium-137 was deposited in mainly upland areas of Wales, Scotland and England where it seeped into the peaty soil used mainly to breed livestock.
The European Commission ruled that a maximum level of 1,000 becquerels per kilogram (bq/k) of radiocaesium should be allowed in sheep being reared for meat to safeguard the consumer. Similar guidelines were given for fish affected by contaminated rivers.