If you were awarded the PJM medal, as George rightly says, for services between 1957 and 1966 then if serving, no permission has been granted to wear.
If you are not serving, which I understand you are not, I cannot see the problem in adding a medal which you were awarded to your rack, just as themonsstar has done. I think they look great.
I think what annoys people is the proliferation of self-awarded, privately produced medals that are appearing on the market (Normandy medal, National Service medal, Hors de Combat medal, Queens Golden Jubilee Commemerative medal [not QGJM] British Nuclear Weapons Test Medal, Arabian Service medal, Active Service medal, General Service Cross - To name just a few) that some people tend to wear in abundance across, and up and down their chest.
Just my opinion. I wear my medals with pride.
regards