GameSpot yesterday posted an interview with BBFC examiner Jim Cliff, discussed primarily was of course the Manhunt 2 banning. The bad news for the UK is they believe the appeal will run into next year, and finish next year at the earliest:

Can you tell us a little about the decision to ban Manhunt 2?
This is going to sound like a cop-out, but I can't talk about it because it's under appeal. You know they submitted a modified version and had that been passed, then obviously I would have been able to but I can't right now as it stands. Sorry!

When is the appeal likely to finish?
Sometime next year, I really don't know specifics unfortunately.

However if your looking to import the game from the US:

Just as a theoretical thing, Manhunt 2 has been rated as an 18 in the US. So if I imported a copy of the 18 version, would I be breaking the law?
No, but if you sold it to anyone, then you would be.

So you are legally allowed to import it, remember though that you will require an American console, or a legal work around such as SwapDisks (Swap Disk Magic) which play NTSC games on PAL consoles and so forth. I'm not sure on how legal importing is for Australians is, as in the past games such as the banned Manhunt predocessor (Manhunt 1) has been banned from imports too. Good luck with whatever you choose to do, and be sure to let us know if you have any luck.