In case you've all forgotten, it's the time of year when some of us remember that it is the anniversary of the Battle Of Britain, when the Royal Air force Fighter Command saved the country from invasion from Germany. At this time of year, most Stations celebrate with a cocktail party, often including a sunset ceremony with a flypast of a suitable fighter, like a Spitfire or Hurricane. Wyton managed a Spitfire followed by a Tornado. Cottesmore and Wittering usually field a Harrier.
Hence all the lone fighter flypasts at about 6-ish on Thurs/Fri around this date.