On the BALPA forum it looks like the guy involved in this case has asked the CAA directly the question about FDP. Apparently he wrote to the head of the CAA
"Is the requirement for an Operator to ‘ensure’ the ‘Flight Duty Period’ (FDP) conforms with E.U.Ops 2.2 (ANO)
a) At the ‘Roster Stage?’
Or
b) On production of the ‘flight plan’ (PLOG) that is produced before report time that is ultimately signed as a legal document by the Commander.
E.U. Ops states an operator must ‘ensure’ ‘that for all its flights. Flights are planned to be completed within the allowable flying duty period taking into account the time necessary for pre-flight duties, the flight and turn-around times.’
For all professional pilots we now know exactly the answer and where the CAA stand because the response he had was from the CAA legal division.
The CAA's official response
''We will not offer an interpretation of a matter of academic interest"
I have written to ask. Maybe if enough of us do we might get an answer.
I think the question is does answer is that it confirms what we have all suspected all along re CAA and the airlines.