No one seems to be answering you Sunny so allow me to volunteer my limited knowledge.
It is dependant upon what ATPL's the schools is offering.
If they are Australian, then they are not valid in the JAA or whatever it is over there system, and you will have to do them again when you get home. Much more intensive and difficult than Aussie ATPL's I believe, and the Aussie ones aint no picnic in the park either.
I suggest you ask the school which it is, and don't take their word for it get it in writing. Also don't let them tell you it is a simple conversion proceedure as this is simply not the case. From my knowledge Aussie ATPL's are worth naught in the UK, and you could be back to square one, albeit with an Aussie CPL when you get back.
Also do your research on your chosen school thoroughly. As with most schools around the globe, they a partial to stretching the truth, and/or neglecting to inform you of hidden costs etc. Ask for all up costs including landing fees etc, and also ask/demand referees etc, ie: past students.
Be sure you are getting what you think you are getting. For example, is the instrument rating inclusive of flying time, or theory only ?
Lastly, why not try the Dunnunda and Godzone forum down the bottom of the forums index. You will probably get more local info there than Wanabees, and chances are some good feedback on the school you mention.
Hope this helps.