Here is my take on it.
UK Top Gear is heavily crafted/scripted pre-planned. Almost nothing that happens is an accident. The trick is they try to make it look as casual as possible. If you take any a-b races they do - do you really think they set up 20 million cameras on the route to capture the drive-past. They have to stop, set up cameras and record the simple drive past. Clearly there is no real race, no matter what you think. But the programme is always defended as an entertainment vehicle it is no longer a motoring magazine, and whilst I find some things a little too co-incidental, you can't help admire the way they portray the schemes.
The reason that Topgear works is their attention to detail. Other motoring programmes would dearly love to get at the assets and production budget that the BBC can throw at it.
If Topgear UK had done that challenge, they would have had some idea of some something to say during the drive, mentioning pimps. drug dealers, the state of the car etc, plus some witty comments on voiceover. I felt they just laughed, and hadn't really got a plan. I may be doing them a dis-service - if so I apologise.