In an adversarial system like the US and the UK each side in the case is expected to put up the best argument possible presenting their side of the case - it's not about them presenting the "truth" (although they obviously can't lie).
I read a passage on a standardized exam once that led me to believe that of the US and UK, only the US was adversarial, and the UK was more inquisitorial. The point of the exam passage was the contrast: in the UK, for example, both sides had to present all of the evidence they had. Not so in the US. Perhaps it's more of a sliding scale between the systems than a dichotomy.
Now, I have to admit I never followed up on this, maybe the passage was fictionalized.
US and UK have pretty much the same legal system. The French legal system is inquisitorial and pretty much all of Europe or is it the world except for the common wealth?
