A senate official has said that a laboratory test confirmed a letter to the Senator contained poisonous ricin, according to the Associated Press. More tests are expected, the official added.
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Another cold, frosty and foggy night for many. Northern and western areas will see thickening cloud, patchy rain and milder temperatures.
Temperatures have already plunged to -12C in some parts of the UK this winter - but Thursday could be the coldest day yet.