^
You're talking about BA here......
Almost none of their flights now operate out of LGW.
"Interestingly" I did a bit of online research. If you check flights to certain destinations that were originally scheduled to depart from LGW but have been re-routed to leave from LHR, they generally show as "on time" on the expected day of departure, but looking ahead to the next day or days, they flag up the flight as "re-routed, check with airline" message, when it does indeed appear that the re-routing is "simply" that they have been changed from LGW to LHR