Franck Muller Vanguard Yachting - David Tennant - Good Omens
The watch has a steel case, black/blue dial and black strap. This model comes in many variations, but it's possibly the V 45 SC DT YACHT NR model reference.
Franck Muller Vanguard Yachting watches costs anywhere from $6500 - $20,000 depending on the variation, but this one you should be able to find for around $7500 for example on JomaShop.
In Season 1 of Good Omens, David Tennant wore a Devon Works watch.
Thanks to Sylvia for the alert