Happened over a week ago.
The crew didn't notice anything until another aircraft passing them as they taxied in at Birmingham piped up that part of the engine cowling was missing. Tracing back down the route prompted contact with Jersey ATC, who had found part of an unidentified cowling on the runway. Time from departing Jersey to landing in Birmingham must have been what, 40 mins?
But then, why would anyone perform anything other than routine runway inspections if no-one has reported anything untoward? Therefore it's perfectly possible for something to remain undetected in the darkness for some time.