Thanks Starcat,
A Munitions search on Yorkshire led me to Barnbow, being the biggest factory in the area, 16,000 people working there and 90% women. There was a disaster in 1916 with 35 women killed, so there are quite a few pictures of workers in this specific factory.
Their uniform is very similar, a full dress overall with a large v neck or buttoned-up. Most of the others I found on Google were women wearing trousers and a overall skirt.
I'll take this back to my father and see if he remembers anything.