Britain’s mild spell is about to come to a shivering end as a ‘major’ cyclonic storm system clips the country. Temperatures will plunge ahead of the weekend as a plume of bitter air sweeps in from the Arctic, driven by a shift in pressure systems spiralling the UK. The dramatic U-turn, as Britons cast off their winter coats, has raised fears of a wintry Easter, with even the risk of snow. Low pressure currently in steering balmy 18C southerly winds will shunt to the north, thrusting temperatures in parts below freezing. Jim Dale, senior meteorologist for British Weather Services and social com…