Capitalization

Can anyone answer this for me please?
When do you capitalize names of professions? For example: would Doctor Basil have a consistent capitalized Doctor throughout a manuscript, and if so, when would the proper use of lowercase doctor be applied.

Same with constable Fisher. As his name is Constable John Fisher, is this lowercase c or capitalized C (as it's his name).
It seems there's a lot of conflicting information on this subject and it's hard to pin down exactly what's the right way to capitalize names.

Thanks in advance.
K