UK JAR PPL SEP which had just passed its 5 year currency
SEP does not have a 5 year currency, or validity, it is 2 years. The Licence has to be re-issued every 5 years, and as long as you have a valid medical, its simply a case of sending a form to Gatwick
http://www.caa.co.uk/docs/33/SRG1102FF.pdf. Mike Gill in Adelaide is a JAA Examiner.
can I have my UK IMCR revalidated by a non-UK JAR IR(E)
No because nobody has the authority to sign the page and probably won't be aware of the content of the test anyway. You could apply for an examiner to do it, but would have to convince the CAA that he is fully conversant with the rating.