Mr angry.
According to my sources - the pilots fly for both airlines, whether based at MAN or LGW (Flyjet LGW now closed so pilots commute to LTN)
MAN based pilots mainly fly Flyjet with occasional Silverjet flight and LGW??/LTN fly mainly Silverjet with occasional Flyjet flights.
There was no jumping ship from one to the other.
The cabin crew are a different matter entirely though as Silverjet have employed their own as its a different standard of inflight service.