Koeniggseg provided the CCX to market their car because at that time they were just being introduced into the US market officially and Arabs aren't too fond of Koeniggseg either :) For them it was necessary to let Top Gear test the car.
I think Pagani is another brand that let them drive their factory Zonda, not too sure but.
And yeah, as Orion said...the Veyron is a mightily capable car on the race track; combine low center of gravity with the width of it and the width of the tyres and you have almost F1 grip levels, despite the 1800kg weight of mass.