This is a rip of one of the two DVDs included in Top Gear Great Adventures 2 (please buy that if you like this!). It's the director's cut of the Botswana episode featuring commentary from the crew and directors as well as deleted scenes (you can find those after the end credits).
To properly play back this file, you'll need a good media player such as Media Player Classic or VLC. If you use a crappy player such as Windows Media Player, you'll end up hearing both audio tracks (the normal one and the commentary one) play at the same time rather than one or the other.
Cheers to our pals at FinalGear.com who which we are not related but are big fans of.