The Department of Transport has mandated what they call ASM's - added security measures - that restricts the availability of access to the flight deck from doors close to doors open.
Having a flight crew licence or in fact an ID from another carrier won't work unfortunately.
Some bureaucrat from CB has made a decision as a result of political and or popular pressure and we must abide by it.
It sucks really, but we are legally obliged to abide by it.
The annoying thing is that these ASM's can be introduced without having to pass through parliament - they are a dictate from the mandarins and there is no appeal.....