Thanks everybody for your helpful comments.
Must admit I'd overlooked SIA and QATAR.
According to web sites, cheapest fare is QATAR but downside is two en-route stops.
Emirates, Etihad and SIA have one en-route stop, and are broadly similar, 'Y' fare wise, give or take $A100. Ethidad has a longer lay over at an airport not noted for its creature comforts.
The clincher for me is that SIA offer the A380 on the SYD-SIN leg around the dates I want to travel. Must be worth trying, if only for the experience.
Thanks for the comments about UK petrol prices. I'll opt for a Ford Ka or something similar.
Assistance greatly appreciated.