The UK has changed to EASA but it won't make much difference to the conversion.
If you're planning on going modular in the UK, I'd just do the CASA PPL and have some fun flying around.
The PPL is relatively easy to convert whereas the professional licences, not so easy.
(read expensive)
You'd also have to factor in the IR - that's usually the most expensive part.
As you'd need to do all the Australian PPL and CPL subjects before sitting the flight test, that's a lot of work for only 1 year. The CASA CPL doesn't really touch on the ATPL stuff. (Well, at least it didn't when I did them a long time ago)