There are several stories similar to the 1 above from
@Chris375.
Some people wearing decent watches being mugged for their watches after visiting Selfridges where several high brands of watches are sold, others being approached in pubs by a stranger who admires the watch and asks if it is a real Rolex, Omega etc.
As a balancing comment, I lived and worked in London for many years, often travelling home late after the pubs shut and didn't even consider that I might be stopped for my phone, watch or other valuables. However it's a big City, things happen here and there and it could be that some young oik who isn't "a professional" and doesn't know a Timex from a Rolex might consider that a new looking shiny CW looks expensive and therefore that they could be onto a soft profit. A recent CW release on a bracelet might have cost you £1000 so can be considered "expensive" in my mind.
If I'm going to London, know that I'll be out late after a few drinks and possibly travelling home on my own then I'd wear a dressed down version of a watch (I think a strap tends to be less noticeable than a bright shiny bracelet) or wear my nondescript fitness watch, which isn't an Apple watch.
Good advice has been given previously .......
"Just be sensible and enjoy your visit."
"....when in a major city just be careful and have your wits about you."