A Spitfire pirouetting overhead, Union flags everywhere you look, a chorus of Jerusalem and of course, rain. Bucketing rain. Is there anything more wonderfully British than Leeds Castle’s Classical Concert? For more than 40 years crowds have been trudging through the stunning medieval grounds laden with picnic baskets, camping chairs and even candelabras for the event. Most people we saw also had umbrellas. “Leave it in the car, I’m sure the forecast said it would be fine” I’d insisted, confronted with the choice of carrying that or jettisoning the scotch eggs. Fast forward an hour and I’m tuc…