Hello Nigel,
The first thing is the visa that people are entering on. If It's a
PR visa, then if they intend to come to Australia for greater than six months (this is the main test but there are others), then Australian CGT will apply, as well as UK CGT. If they are coming for less than six months, then no issue. Hence, a "recon trip" to Australia is fine and I think this is what your migration agent was talking about at the seminar.
If you don't come in on a
PR visa, then there's no Australian tax implication at all.
If you are an Australian tax resident, then if you have more than A$250k in a bank account overseas, you have an issue. Australia will seek to tax the foreign exchange rate gain. Now, if you sold a house, for instance, and then left he money in a UK account, this issue could occur.
In terms of just transferring money between the two countries, ordinarily there is not an issue from either end.
There's a whole of rules that come into play with cross-border issues and UK migration agents (even if they are an expert in that field) are being negligent by offering complex tax advice, covering two tax jurisdictions.
Cheers, Andrew