all you blokes shocked by the law etc etc - think about it for a minute.
it's all set up so that people DON'T do what the OP is trying to do (ie: bring car over for a big profit)
the law is setup for those that live oversees, love their car and want to bring it home.
they then want the costs ideally to be only *just* less than what it would be to replace, so yes, you'll do it, but no, the goverment won't lose out on the money they would had you left it behind and then purchased the closest equivalent when you emmigrate back to Aus.
it's generally ONLY ever worth it if the car is one you have O/S and you actually do *need* it whilst there.
owning a GTR or Porsche or whatever for 12months is a massive cost in itself (insurance in the UK is horrendous, plus it'll be parked outside more than likley and get covered in dings, scratches, bird shit, salt etc etc)
So unless you can justify owning it and using it - it never stacks up. the idea of buying something and sticking it in a garage for 12 months for the sake of 10-20% profit (ABSOLUTE best (realistic) case once ALL the costs are taken into account - ie: the garage for a start!) is ludicrous and not the best use of your money for 12 months+
and remember, it's a risk. you might make 20%, but you also might make a loss pending market, currency change, import rules changes etc - so you need to accept that risk as well - 12months is a long time.
my 2c.