The shopworkers' union Usdaw received boos at the TUC conference when it announced that it was opposed to the motion looking into a General Strike.
But Usdaw said the action would hand the Government "the biggest stick to beat us with".
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Michael Fallon has received reassurances from his US counterpart that security ties with Britain will "endure" following a vote for Brexit.
On Friday, police said it appeared the girl had shot herself in the face with the weapon.
The showers will be slow-moving, heavy and thundery at times, particularly in central and eastern areas.