You will probably disagree with this, but I think the most destructive thing that Britain ever did to Australia was not to test Atomic bombs there. I think it was exporting rabbits. According to one American author we exported about 7 there back about 200 years ago, so some silly bastard would have something to shoot at whilst sitting on his porch. After they escaped, rabbits basically did what rabbits do and wreaked havoc on the natural environment. Supposedly disease culled the numbers in the 1970's again, but not surprisingly numbers are worse than ever.
Compared to Roger Rabbit and his friends, Blue Danube was small beer when it came to the Australian environment.
British testing for atomic bombs and rockets was actually a major driver for the building of dirt roads through large, hitherto almost unexplored parts of the Outback.
The bombs didn't leave much behind in terms of long term radioactivity really. You can visit the test sites today if you're so inclined and they're absolutely fine.
As I understand it most of the worst contamination came not from the big bomb tests but the "minor tests", like setting a chunk of plutonium on fire to see what happens if a bomb burns, or blow up a bit of uranium to see how it disperses, and so on.