Originally Posted by corporate-wage-slave

That was not risky and the thing that is perhaps missing in your account is the nuts and bolts of how LHR-GOT and LHR-SIN-SYD works. So there wasn't much risk to SIN-SYD given the way aircraft are rostered on that route. The risk point was a commitment to GOT-LHR with an 18 hour margin LHR-GOT. LHR-GOT-LHR always runs in that fashion, but in the 18 hour gap here there was no realistic alternative given the very limited options to GOT and the fact the limited SAS alternative often runs full. So 18 hours could have been a margin of 20 minutes. On the other hand arriving in GOT you are held in a gate area after leaving the aircraft so if doing a true back to back you get off the aircraft, sit at the gate, get back on the aircraft. No security, no passport check, very easy. So adding 18 hours time "fat" is adding risk. The OP did this because they had checked luggage, which isn't something I would do, but the way around that is to split off LHR-GOT-LHR from the sectors to SIN and SYD, or to store the bags at LHR. Both have a cost, and one option would probably require an agent to construct the ticketing, so it's a money versus risk trade off plus a bit of convenience of booking, convenience of checked baggage.