I did something similar myself. I started my PPL at Bankstown whilst working in Australia back in 2001, did my GFPT, and passed all the theory exams, and did the solo Nav flights. Unfortunately, I had to return to the UK earlier than expected - before I could do the PPL test.
I phoned the CAA from Australia before leaving and explained the situation and the person I spoke to said it wouldn't be a problem to credit the hours (can anyone guess what is coming here...?)
So back in the UK I asked the CAA what counted - and the best that I could get was a credit of 15 hours. At the time, I had about 50 hours logged and wasn't all that happy with the idea of most of my flying to date not counting; so I ended up going back to Sydney 18 months later for a month to do the test and get the PPL issued. Moral of story: get anything from the CAA in writing - although I've heard that this can be easier said than done.
Problem with Australian license is the "quick trip" down under every two years to do a BFR. I've never found any Australian instructors in the UK who can do it (there are, however, plenty of doctors around especially at Gatwick and Heathrow who can do CASA medicals if you want to keep that up to date).
I am now literally in the middle of getting a JAA PPL - and this is straightforward as others have said. As I have over 100 hours, I've just had to take Air Law and Human Performance theory, and I'm doing a skills test next week. Presumably I then enjoy a trip to Gatwick with every bit of avaition paperwork ever issued to me and I leave with a shiny new license, but we'll see how that goes
I think that it was a benefit to learn initially in Sydney. For example, I didn't know the area and therefore I was forced to actually learn to navigate properly rather than being able to look out of the window and say "Ah, that is Brighton" or similar. Also, the prevailing attitude to GA in Australia seems to be (or was then) that its a damned big place and you're learning to fly so you can get about - it does appear that flying a light aircraft is seen as a practical tool rather than something you do on a sunny Sunday afternoon once a month. The airspace around London is more congested than that around Sydney, but it gave me a good introduction to what was needed in terms of RT use, planning for control steps, etc. The scenery out over the Blue Mountains is fantastic of course, too.
Good luck with whatever you do - but I'd try and do some flying in Australia, its a great experience.
Paul.