BA have for years done that down to SYD (and before also to BNE, MEL, PER) from SIN.
ie LHR-SIN (4 crew, 48 hours off)
SIN-SYD (2 crew, ~34 hours off)
SYD-SIN (2 crew, 48 hours off)
SIN-LHR (4 crew)
Maybe it's time to look at those agreements. Better to do that and maybe keep the LHR leg in-house, surely?