I can find no reference in any ICAO annexes, UK CAA documents, UK ANO, or JAA - JAR OPS 1, that refers to a position of "Captain". All references to the pilot in charge of an aircraft are to the "commander'.
The term "captain" in a company mis-use of the correct reference to the 'pilot in charge"of an aircraft.
I guess if you are a serving member in HM forces (for Brits) and have attained the rank of Sqdn. Ldr in the RAF, or Capt. in the Army you are entitled to use the term captain, much as a "Dr". or "Prof"is entitled to use these titles when they have qualified to do so by means of academic attainment. Is there a minimum academic standard for a pilot in charge of an aircraft?
IMHO the answer to your question is that the title should be dropped as soon as the "captain" finishes his/her duty period, and thereafter when he/she comes to the end of their flying (in command) days with the company.
I trust this will evoke some spirited response from the flying community!
