While I understand that this segment of theirs was a joke, it did have a point to it. They were trying to show that it is possible to drive a Prius in such a way that you don't actually save any fuel over a non-hybrid.

I don't think anyone would dispute that a Prius is more fuel efficient than a sports car in stop-and-go traffic and having that segment on Top Gear just wouldn't be possible as it would make the show "fair" to the hybrid and actually about cars which it definitely isn't.

And I think they make these silly claims at times since they know they are so over-the-top that it's hard for anyone to take them too seriously.