Pattern 60 DPM is the immediate predecessor of the more common Pattern 68 combat smock. It is notable for the concentric stitching on the collar, “pen pocket” on the upper right chest pocket, and pleats on lower pockets, all of which were not included in the later Pattern 68 smock. These smocks were produced between ~1960 and the early 1970’s (source: http://hmvf.co.uk/topic/24552-1960-pattern-dpm-smock-size-9/). There are no sleeve pockets unlike later combat smocks.
Size tag is missing but is like Small-Short. Tapes are for a US Marine with a Marines Parachutist wing, perhaps it was used on an exchange program or traded in an exercise. The US BDU buttons were added to the inside to allow an M-65 type liner to be buttoned in. Very heavily used.