Originally Posted by Globaliser

This will almost certainly give the OP what he needs, but to be technical, this is not the fare basis. That single letter is the booking class (or "selling class" in the MMB display).

You'd need the full fare basis - which contains perhaps half a dozen or so characters - to get the full rules for the fare. However, the booking class alone will almost certainly do the job if the OP did indeed buy an I class fare.