biggles72, here is the real story.
To fly a G registered aircraft (UK reg) for hire or reward you will need either :
(1) A UK CPL/ATPL; or,
(2) A JAR CPL/ATPL; or,
(3) A foreign professional flight crew licence which has been validated by the UK CAA.
New UK CPL and ATPLs are not being issued any more, although UK CPL to UK ATPL upgrades are being issued for the next 18 months for people who have already done the UK national written exams.
You can go and do a JAR licence but it will cost you a lot of money, time, heartache and frustration. You should be well aware of the principles of wooden airframe construction and stellar navigation by the end of it though. (ie its a load of useless crap) There is effectively no "conversion" to a JAR licence from a non-JAR member state licence. You have to do 14 written exams and two or three flight tests just like someone off the street with no experience at all. You will also effectively have to do a 26 week ground school at an approved flight school.
Or, there is the licence validation route. You can fly a G registered aircraft for hire or reward on an Australian ATPL as long as it has been "validated" by the UK CAA. The validation process must be initiated by an employer, you can not seek a validation on your own (unless you are also a UK AOC holder). The process costs money and time for the employer and you must hold any needed type ratings on your Australian (or other foreign) ATPL. You are in fact flying G registered aircraft based on your Aussie ATPL.
Unfortunately, one of the main reasons why most Aussies volunteer for the lower standard of living in the UK is to seek career advancement onto larger equipment. Here is the trick part, I dont think that any airline will go to the time and expense of trying to organise a validation for you unless you already have substantial time on the type of aircraft they are operating. And while you are on a validation you are tied to that employer and aircraft type. So you dont actually get any career advancement out of it - at least not initially.
Then there is the process of converting the validated foreign licence to a JAR licence. You still need to do all 14 written exams, although you will probably be able to get out of the 26 weeks ground school. You will avoid the expense of the two or three flight tests since your sponsoring airline will have put you through those flight tests in the simulator.
Despite the fact that some UK airlines are parking jets because they cant find captains for them and none of the first officers have enough experience for command, the local unions are opposed to the idea of foreigners flying in the UK. Unless, of course, the year is 1918 or 1942. The word xenophobia does come to mind. You should expect quite poor treatment from the natives when you arrive and during your stay.
So, in short, YES you can get a job and can fly in the UK on an Australian ATPL, but ONLY if you already have substantial time on type and can get an employer to sponsor a licence validation application.
With regard to the right to live and work in the UK, you will need to organise this yourself before an employer will offer you work. The fact that Australia is a member of the Commonwealth of Nations is of no benefit to you in this case. The fact that UK airlines are parking jets due lack of experienced crew is also of no benefit to you with regard to work permits. In order to be allowed to work in the UK you can :
(1) Be a UK or EU citizen yourself; or,
(2) Choose your parents or grandparents (UK citizens); or,
(3) Choose your lover (marry a UK or EU citizen).
Best of luck with it all.