A flip-flopping jet stream will rescue Britain from the autumn chill ushering a fortnight of glorious warmth. The UK weather is about to undergo a dramatic makeover with temperatures set to soar this weekend. Arctic air swept in by a southerly jet stream will be blown away as the channel of fast-flowing air circling the globe shifts north, opening the door to balmy gusts. High pressure – the gift-giver of summer sunshine – will build from the south and east through the end of September. Met Office meteorologist Annie Shuttleworth said: “It is set to turn much milder as we head into the weekend…