Something to consider: If you gain an Oz or FAA CPL + IR you will have the advantage of doing most of your training at the cheaper rates. It also means that on the return to the UK there is no minimum training requirement before sitting the CPL flight test and only 15 hrs required for the IR test. For the old UK national licence you were also excused from having to do the morse code & radio practical tests.
You would still have to do the 14 ATPL exams but that's pretty unavoidable. Don't forget the JAR ATPL exams give credit for the CPL too, unlike Oz or the US. Caution though: Unless you have the hours for the ATPL to be issued you will have to keep your IR current to maintain the ATPL exam credit for when you eventually reach the 1500 hrs.
Unless things have changed you can also save a bundle on the UK Class 1 medical. When I converted to the UK ATPL I was able to take advantage of a procedure that gives some credit for holding a foreign professional licence + class one medical. I've forgotten the details (it was nearly ten years ago so things might have changed) however it involved arriving in the UK with a current Class 1 (duh), an audiogram, an ECG, chest xray & maybe an opthalmologist report. The UK CAA may have sent a form to me to have the Dr complete too. Having all of that done meant that I could transfer my Oz Class 1 instead of having to go through the whole UK initial issue crap.
A lot of the medical stuff in Oz I was able to do under medicare by getting a referral from my GP. All in all it saved hundreds of pounds. You would need to talk to the CAA medical branch to see whether this option is still available.