As a follow up...
In the end, I decided not to bring the car as it was too much hassle / potential risk alongside actually emigrating. We decided to give it back - you could do that on the lease there, you just have to get you local dealer to give you a price and hand it back. However, in the UK, the market was such that the dealers would not even take GS430s (mine was perfect condition, FLSH and 40K miles) as they could not sell them. We negotiated with an embarrassed Lexus UK who agreed to take the car back themselves and did us a reasonable financial deal.
We arrived just over a week ago and have been car hunting, as one is needed urgently for work. We tried the following - 2008 Toyota Aurion Presara (not bad, many of the same gadgets as a Lexus, and loads cheaper but front wheel drive); 2006 Audi A6 wagon Quattro (expensive, hadn't worn very well and hard suspension); Subaru Liberty 3.0R B spec and STI (not bad actually, especially the STI - but a little too focussed and too much of a compromise); BMW X5 3.0d and 4.4i (not bad at all, but expensive and poor spec comapritively); Lexus RX350 (not bad, but not as good as the GS) and lastly - what about two cars Impreza STI plus Presara (too complicated, maybe another time).
Guess what we went for in the end? 2007 GS430 with 14K kms, cheapest in Australia at nearly $60K off original list. That will be GS number 5 and it will be a keeper at these prices!! Interestingly, at the current conversion rate and in the current climate, it is actually cheaper than my original car cost me in the UK and is a better deal than importing - nevertheless a fluke I think!!
Cheers,
Marcus.