This is kind of a Thankyou to James (Mr Hans) for the helping me sort my Seb problem.
I bought a secondhand Seb2 chip for my Gt3 and found it wouldn't even attempt to start so I took it as a dud and bought a brand new one from Mr Hans. I fitted this and it still wouldn't start so I had a poke about and found it wasn't fuelling or sparking :S. After double checking everything Mr Hans suggested I needed a Decoded chip due to the immobiliser cutting in and not allowing it to start.
I received the Decoded chip yesterday and the car started straight away so hopefully this should help someone else having similar problems.

My car was running the correct Gt3 ecu for the Gt3 engine so it seems it was the aftermarket alarm causing the problems but i'm sure Mr Hans will correct me if I'm wrong.