London’s summer season of events—which dates back to the 17th century, when aristocrats brought their marriageable children into the city for socializing—begins with the Chelsea Flower Show, but it really takes off in June with Ascot, the Trooping of the Color, the Henley Regatta and Wimbledon. For all Anglophiles heading across the pond for these rituals, or just for a British fix under summer skies, there are lots of buzzy openings to know about. Read on to learn what is soon to open; what I r...