Is this an Australian Dog tag?
 

Hi, not sure if this is Australian. Any help appreciated. Cheers Karl

Not an issue Aust Army dog tag that I am aware of Karl. Might be RAN or RAAF however the prefix P/MX doesn't ring a bell. Keith

Ignore

I believe that the disc belonged to a member of the Royal Navy.

The P, for Portsmouth, being added in 1934, and the X to show that the man in question was in receipt of the (lower) post 1925 rate of pay.

The JPEM stands/stood for Junior Provisional Electrical Mechanic.

I had to google to find out exactly what JPEM stood for, and found this interesting account of a JPEM who took part in the D Day landings, carrying American troops to Utah:

https://www.combinedops.com/HMLCT%20795.htm

Hi Keith, Many thanks for eliminating Australian angle. Cheers Karl

Great work BWEF. Mystery solved I think, with an excellent link to boot. Many thanks, Karl