"...An RAAF aeroplane.
Will any information on that machine be available at Kew, or would it have gone to Australia?"
No, the aircraft records will be in the UK. If it was an RAAF Squadron's aircraft, then the Australian War Memorial will have (copy) ORBs for the unit, available for research, I believe, but originals as you've found in the UK. Interesting results from the general search on the AWM website:
Search | Australian War Memorial And:
466 Squadron RAAF | Australian War Memorial
Personnel records will be available for RAAF Personnel through the Australian W.W.II Nominal Roll. Hope that helps.