RAC wouldn't attend breakdown

Askfirst

If this is RAC’s response to a policy holder being stranded with an incapacitated car, through no fault of their own, I would question why have the cover in the first place. Been a member for decades.  Will be looking at Ts and Cs very closely in future. 

BoGoF

Susan82 said:

I'm not entirely sure how far you can push "mechanical failure". They don't give a definitive definition, instead they give some examples (the engine not starting or electrical failure). I would consider anything that breaks on the vehicle which stops it from moving to be a mechanical failure (as the whole vehicle is a 'machine'), personally... 

What you consider isn't really relevant I'm afraid. The undertray is not a mechanical part that prevents a car from starting or driving, in fact a car can run without one. So in that regard it's not a mechanical breakdown. It's very unlikely the undertray would become dislodged without hitting something.

Keep_pedalling

The fact that your insurer recovered your car rather backs up the RAC’s position that this was accidental damage not a breakdown.