would it be feasible?
Does the B777-200LR ( for that's what he means by 77L ) actually have the useful range to do this with payload. I know QANTAS managed to do LHR-SYD with an empty B744 years ago but that was towed to the runway threshold...
It's worth remembering that the yields on London-Australia are pretty poor, hence the slow withdrawal of BA from the region. London - NYC is a connection of two world banking cities, London-OZ is a Hell of a lot of low yield leisure traffic without the big bucks down the front end.
There are two B747-400s at CWL in storage ( G-BNLB / C ) with a B777 under post delivery checks with another one due imminently. ( G-YMMR / S )