Hi Doorisarmed,
Im a fellow paddy in BA. Im not sure what "intermediate Cert" is as I believe they have changed the whole exam thing in ireland since I left school in 99 but basically you need to have reached Leaving Cert level and passed at least Ordinary Maths and English!!! Hope that solves your query and good luck with your application!!!
P.S...Even if you have not reached that level still send off an application as a friend of mine failed maths in the LC and she was still accepted because of her wonderful personality...
!!! Anyways, you need only really worry about maths when it comes to counting that you have the correct number of meals onboard (amazing still how many people get that wrong, haha), as for duty frees, its all automatic and only CSD's really need to worry about calculating crew hours!