Precisely this^
I really don't see the need to accelerate to close a gap and end up having to slam the brakes on to prevent a crash, which inevitably ends up in having a crash anyway.
In hindsight, had the OP's wife maintained her speed, or even slowed down to let the Audi slip in without affecting her life in anyway shape or form, would have prevented this.
You cannot prove that at all - it's all supposition.
The fact of the matter is the driving was poor by all parties, but the fault is still that of the Micra driver - he/she is the one that hit the car in front.
Nobody is saying she should have let the Audi out. The Audi had nothing to do with the collision and shouldn't be considered in that way. It was a potential hazard at the side of the road. The question should be whether or not it is sensible to deliberately and aggressively drive yourself toward that hazard?
As for your final comment, the same is applicable to the camera car.
Not really, as the camera car didn't hit the car in front. So, although poor driving, and sudden braking still stopped in time.
The point is:
The micra left the scene of an accident - this is the issue, irrespective of the Audi, or the erratic driving up ahead, the accident is still as a result of the micra being too close to the car in front. This crash
may have avoided the accident had they let the Audi in (which they had no need to as per the highway code, as it was pulling out onto a main road) and/or had they driven less erratically - that is pure supposition. And most of this is irrelevant.
Yes, the driving standards were poor, yes perhaps they should have let the Audi in, yes it
might have avoided the accident, but the fact is they didn't.
Complaining about the standard of driving doesn't detract from the fact that the OP has been involved in a hit and run.