Many thanks cymro, layz and for the clarification c-w-s.

I think given the rules it would be best to stick to a BA flight hence not going for the AY flight.

I might actually use avios to book, worth making sure the SYD flights are included in triple avios rather than a pair of SH flights.

I'll have a look for availability once I'm home this evening.

Thanks once again all, #FTRocks