The logic is so flawed here, we don't know where to begin. According to Davies, giving a car more power makes it heavier, thus increasing the amount of CO2 it emits. First of all, cars are heavier these days primarily because most developed nations, Europe and the United States included, have federally mandated that cars be made safer, and to achieve this, manufacturers have had to design new safety systems that add weight to cars. Things like airbags, crumple zones, side-impact bars, and the like are the primary reason cars have gotten heavier. While enlarging the displacement of an engine, switching from four to six cylinders or adding a supercharger could make a car heavier while giving it more oomph, more power for its own sake is neither a necessary nor sufficient condition for a car gaining weight.
And that's just it, most mainstream vehicles don't get power bumps just for the hell of it. Additional horsepower is usually required to comfortably move the additional weight added by the aforementioned safety systems. Yes, there's a vicious circle here, but Davies' logic is completely backwards. By his logic, Europe should actually ban all safety systems in cars, because as cars have gotten safer, they've also gotten heavier and are thus emitting more CO2.
And of course, Davies must realize that even if the unthinkable occurred and Europe banned cars that were capable of more than 101 mph, unless the law was written to specifically preclude this, automakers would likely just use a governor. After all, a Bugatti Veyron with a governor that drops anchor at 100 mph is a car not capable of 101 mph.