Occasionally I've noticed the RED ALERT warning by the front collision warning system.

 

Does it also break automatically and in what conditions does it decide to brake?

 

I don't want to test it by driving into a wall for obvious reasons.

 

In my experience, auto braking is a last resort, such as when reversing and it senses a pedestrian or vehicle. I happened the other day as I was reversing from a space in Tesco and an idiot exited a space opposite to my left and turned past the back of the car. It was a BMW driver so naturally he had the right of way. 
 

I’ve had the front warning come on several times and it did brake once when I was weaving between cars in a narrow road. I was able to override it immediately by keeping my foot on the accelerator as I wasn’t in any danger of hitting the parked car in front of me.

+1 to wat @numskull said above.

 

my front assist won't brake immediately, but if don't react with a couple of seconds, it will hit the brakes.

 

my rear cross traffic alert on the other hand is trigger happy and will hit the brakes if a bird flies anywhere in the rear radar vicinity!!

Yeah my rear does my head in. Slams on the brakes when I’m reversing out of my steep driveway.