Mysterious black ring seen floating over England (Update: never mind, it was just a fireball-shooting trebuchet)

"It was just floating there like a cloud" []

Fission Chipz has the most convincing explanation so far: transformer explosions.

Update: The BBC reports that it was in fact nearby Warwick Castle testing its fireball-shooting trebuchet, which is basically as badass as this story could have gotten short of a full-scale alien invasion.