A ‘cold plunge’ is about to push temperatures back to freezing as northerly winds blow away the spring warmth. A change in atmospheric pressure patterns early next week will topple thermometers from recent 20C highs. However, winter coats will make only a brief return with warmth forecast to return ahead of next weekend. Thermometers will drop widely from Monday amid warnings for parts of the country to brace for thunder and hail. Lows of freezing could hit the high spots of Scotland and northern England while the rest of Britain sinks to single figures. Met Office meteorologist Alex Burkill s…