We are of english heritage and my father bought it either in England or possibly in Europe whilst in the merchant navy.
Solid 9 carat gold cases are very
common among watches retailed in the UK. I'd wager that's exactly what it is. As C. Hurt said, you'd have to take the back off to confirm. And if you'd like a little more information, posting a picture of the movement might yield you some clues. You're right that it isn't going to fund an early retirement, but it's still likely a good quality Swiss movement in a nice solid gold case. I'd certainly be happy to own a solid gold watch handed down through the generations.
And if I'm looking at the picture correctly, it appears that it has solid lugs. If you end up changing the band to leather, you can get "open ended" straps for this type of lug.