Experience in the jungle during World War II had proved that the traditional fibre identity discs in use up until that period were unsuitable as reported at the time:

The Graves Registration Service in the Middle East reported in 1943 that the fibre identity disc lost its markings after preliminary interment in hot damp soil, owing to the acids and gases generated; that it pealed and became illegible under desert conditions; and that if exposed to intense heat, such as in a burning AFV, it was totally destroyed. The Lethbridge Mission in 1944reported that the Graves Registration Service in the Far East confirmed this. It was therefore decided to introduce for jungle scales stainless steel identity discs in lieu of the fibre pattern; these were fireproof, rustless and non-irritant.

These discs would continue to see service long after the war and this set dates, I believe, to thhe 60s or 70s:

One of the discs is slightly oval and with two holes punched in it, the other circular. The soldier’s name number and religion are punched into the metal. The discs are secured to a nylon neck cord:

The decision to use nylon was the result of extensive testing during the war to find the most appropriate material:

The cotton string as hitherto used with fibre discs was useless as a necklace; it was not fireproof; on interment it became foul at once and rotted in a few days. A fine stainless steel ball chain on the American pattern would have been ideal in most respects, but, apart from the fact that the machinery was lacking in the United Kingdom for the manufacture of fine ball chain in the metal required, the main objection was that chains of this nature were coveted by the Japanese for their personal adornment, and they were not too particular how they removed them from the necks of the wounded. Nylon cord dyed S.C.C.19 or light tan was therefore accepted. It was rotproof, less liable to become fouled and not adversely affected by anti-gas ointment or mosquito repellent. Also there was no tendency to rattle. Its chief disadvantage was that, although the least inflammable of textile materials, it was not fireproof. After the war nylon cords were adopted for universal issue, but attempts are still being made to develop a fireproof article.