Hi, that’s a lovely watch. It looks to me like a Smiths W10, the relatively unusual RAF issued 6B version.
If you want to know everything about it, I suggest trying the Smiths sub-forum of the Military Watch resource website.
https://www.mwrforum.net/forums/foru...Vintage-Smiths
The 6B versions are unusual enough that a register has been set up to record the serial numbers.