The cancelled flight operates on an EU carrier between two countries outside the EU. What remains to be seen and is yet undecided is whether either UK or EU courts (ultimately) determine that the same principle which would apply in the other direction, e.g. LHR-SIN-SYD, would apply for SYD-SIN-LHR where the delay into LHR exeeds 3 or 4 hours as the case may be.