I asked the same question on RolexForums, someone suggested I post here.
I have discovered one of these in a box of old family watches (I suspect it belonged to my great uncle). I was going to get a strap and wear it having worked out the function of it's 24 hour hand (useful to me since I'm a pilot). But having done a little googling and ended up here I see that it's too good for that. It seems to be in very good condition compared to some pictures I have seen. Since it has been in a box for several decades I doubt it has any non-original parts.
Serial number on outside of case is 3222xx
I like it but I do not share the passion of some here!
Who in the UK can I take it to for checking and to verify it's the real thing