"Just spoke to Caterham Tech, and they say that as long as the red light is not on, then the immobiliser is disarmed and the car should run." - sorry to be a pedant, but this is just crap - the red light will be off if there's no battery in the car! - stupid point I know, but it serves to prove that this is a very simplistic answer and the truth is a lot more complicated.
I have an academy car with a Master cutout switch and a starter button. I never leave the cutout key in the car, so I have to go through this procedure every time I start the car...
1. Check that ignition is OFF and gearstick in neutral!
2. Put in FIA key and turn
3. Press the "lock" button on the plipper 4 times with a pause between each press - each time you press it you should hear a "click" from the immobiliser (on the bulkhead above the steering column). After pressing 4 times and having the immobiliser click its acknowledgement 4 times, the relay will click a few more times by itself and the red light will be flashing.
4. Press unlock once and the red light should stop flashing
5. Turn ignition to ON (listen for IACV to burble about, and fuel pump to whine)
6. Press big red button
NB, if when you turn the ignition on the light goes constant red, then you haven't unlocked the immobiliser.
Good luck.
PS where are you, if anywhere near Edinburgh, I'd be happy to help...