Very nice indeed - don't often see then in that condition or size.
I suspect the 'HE 5' stamp is more likely the quality controller stamp number rather than a second guess at size.
You have a large sized smock and a small pair of trousers there - as the 01, 02, 03 sizes were smallest issue size available.
H E Textiles did seem to be a the better end of the makers of that era.