Clarkson goes on to review the Porsche 911 GT3 RS, comparing it to the BMW M4 GTS. Although he criticizes the BMW for sacrificing comfort for no appreciable performance gains, he declares that it better than the Porsche 911. The reason? Hammond owns a Porsche 911 and therefore it must be rubbish.
The presenters travel to South Wales and set out to make the most environmentally friendly car bodies using the platform of a Land Rover Discovery. May makes his car out of mud, Richard Hammond uses plants, and Clarkson uses the bones and carcasses of dead animals.
Prior to their 11 mile road trip, May's mud car falls apart, resulting in him rebuilding the car using bricks which he has to create himself, out of mud, straw and sheep dung, turning the starting field into a small industrial brickworks in the process. While May works through the night, Hammond and Clarkson go to a local village where. During the night, Clarkson's meat car is destroyed by a local dog. He is forced to repair the car with meat from a butchers.
Jimmy Carr is the guest of "Celebrity Brain Crash", but his jet ski collides with a boat on his way to the tent. To fill in the time, the presenters introduce an Audi TT Mk1 Quattro with Hammond hidden behind the rear bumper to show a new smuggling technique used by illegal immigrants, as well as using Hammond as an improvised parking sensor.
Finally ready to begin the challenge, the trio have to ford a river in their cars, which disintegrates the mortar holding the bricks on May's car together. A mechanical hedge cutter almost destroys Hammond's car since it blends so well into nature, and May rebuilds his car again – this time with hay and cow dung.
The three cars are then raced on a dirt track against three normal cars. The idea of environmentally friendly car bodies is abandoned after Clarkson's meat car is infested with maggots, Hammond's garden car catches fire, and May's hay car falls apart.