I've lost the red key for my 2001 S4. I know I should replace the dash at 2-3K but I'm skint. Is there a way to turn of the immobiliser, I have a copy black key but it no longer turns off the immobiliser.

You're not going to like hearing this but unfortunately you're outta luck. The immobilizer system is designed so there is no bypass without some major work. You're going to have to spring for the new dash and keys, or find a complete set off a smashed bike.

Wish there was a better solution for you.