Could BA do what SQ have done and launch a couple of flights, maybe twice daily, non-stop from LHR to SYD with the 77L?
Does the B777-200LR ( for that's what he means by 77L ) actually have the useful range to do this with payload
No, the 77L does not have the range for SYD-LHR with economically viable payload. QF spent a long time evaluating it and Boeing tried to tweak it but they couldn't quite get there.
with a B777 under post delivery checks
Well, mainly cabin installation. Due into LHR to commence scheduled services early June.