Hi Tom,
Just to back up the previous post - Australia doesn't issue JAR medicals as it is not in the JAA!
If you have an Oz Class 1 then to convert it to a UK one (assuming you want a UK issued license) then this link may help:
http://www.caa.co.uk/srg/med/default.asp?page=2576
I haven't looked in great detail but suspect you may be up for 422 pounds up front :-(