Duke of Edinburgh medallion - 70 Years of service

Obtained this item today, along with a few coins that I needed, as it was sold all together, as normally, I would have left it.
Apart form the obvious, (70 years of service), does anyone know anything else about it?

Dimensions
Weight-49.18gms
Diameter-50mm
Thickness-3mm
Came in a very air tight capsule



Will probably put it up for exchange, for Royal Memorabilia collectors.

In the UK, everyone can make those things. Which makes the value not much, exept if you want to buy it.
Can you make a sharp picture of the marks under the head?
Those can reveal more.

I can describe them better than I can photograph that close.
There are three golden rectangles in a row immediately below the Dukes chin
Going from left to right, I will descibe each rectangle.
Left. Capital letters N P, where the vertical of the P is attached to the r/h vertical of the N
Centre. Union flag. No colour
Right. XVII
That's the best I can do, I'm afraid.
Probably, no help at all