This clip is from the latest series of Top Gear btw.
There are a lot of niche manufacturers and tuners out there who claim that their machines could top the Veyron. On the face of it it seems plausible, I mean a lot of these machines have crazy figures and performance.
But, I'd like to see them try. Like James May said, its relatively easy to reach 150mph. The Veyron need around 270bhp to get to that mark. But then to get to 252mph needed another 730bhp. This is because of the laws of physics. The faster you go, the harder the air fights back. Then there is the limits of the other parts of the car, especially the tyres, which on the Veyron can only last for 15 minutes when approaching top speed. Then there's the fuel which can only last for 12 minutes at that kind of speed and so it goes on.
Then the most important point of all is that VW built the Veyron to the absolute highest standards of engineering and quality. They wanted it to be reliable and safe, the reputation of VW hinged on it. At 252mph, the Veyron was absolutely planted and undramatic, almost cruising, not a bit scary. Try that in any other car that claims to come close to these sort of speeds. And VW also made sure that EACH Veyron has and can do all the things that they said it could, without any changes or mods, like the very tyres it runs on the roads. Means that an owner can go for the 252mph top speed if he can find somewhere long and straight enough. Again, try that in some other car with similar lofty claims.