Bad news I'm afraid Gareth, the watch is a really bad fake, or counterfeit, as it should more correctly be called. PS: My commiserations on the passing of your FIL.
Sorry for your loss. Your family member likely never knew it was counterfeit and enjoyed the watch. No harm done there. If you find the who sold him the watch, you should straighten him/her out
Very sorry for your loss. My advice, don't say much to your family about the watch being fake. As long as nobody tries to sell it as real, maybe ignorance is bliss?
Stick around Gareth. I made a bad Craigslist purchase a couple of years ago when I first started and got laughed at. Now a big triangle 165.024, 69 220 Speedy and 1964 Speedy later and I’ve gone full blown collector. Good luck