It would surprise me if BA had an aircraft sitting around for week doing nothing. Does anyone know if there's a reason why it been sat there for a week?
G-VIIL is a 777-200 powered by GE90 engines and is based at LGW. I could be wrong but if I remember right it's a 3-class aircraft.
As far as I am aware this aircraft is going through some overhauling and was rostered to be off the schedule for some time, in fact a LHR-based 777 has been sent to LGW to replace it in the meantime. This is not an unusual thing, it has happened a few times before.
If you need more info I believe the guys in the spotters' forum have more details.
FBW