[spinynorman]

Just to add, "N. K. Co" is the mark of N. K. Watch Case Manufacturing, a company started in October 1937 and named for Nathan Kayman, a jeweller of Russian extraction. According to Priestley, the punch was registered in March 1946 for Szlama-Lejb Ryngelblum and Moisze Libchaber, who were Polish gold and silver casemakers working for the company.

Here's an advert that ran in the HJ in the late 40s and start of the 50s.

I came across them because the company was bought by Excalibur Jewellery Ltd in December 1974. From what I could see, they made gold cases for Accurist, Helvetia, Benrus and others.

 

[spinynorman]

Shame there are no pictures to verify.

You're in luck. From a rather poor scan of the Great Universal Stores catalogue of 1967, it looks like the same watch.

I make 20 weeks at 11/- a week £11. That would be a deep discount from @Eaglegale 's list price of a similar watch, but still gives GUS a profit.

 

[spinynorman]

Great bit of research by @spinynorman.

I'm not sure I agree that it's the same watch. It's similar for sure, but the dial isn't quite the same.

Shhhhhh!