The Top Gear photos show the tires that the Huayra was wearing on the day of the test. Per Pagani's website, the Huayra comes with Pirelli P-Zero tires that measure 255/35ZR19 in the front and 335/30ZR20 out back. The Huayra on Top Gear had front tires labeled as 265/645 19, which is not a normal size for a road tire.
Another Pagani has tires that size. They are Pirelli P-Zero slicks that Pagani says were specifically designed for the Zonda R.
The tires on the car at Top Gear's track do have a tread pattern, but it is vastly different from the pattern on the tires the Huayra is supposed to have. It actually resembles the shallow tread of a Formula One intermediate rain tire.
There is more evidence that these are modified slicks from Teamspeed forum member mattjs33: The tires have indicator dots on them. Why would a tire that is supposed to be treaded need indicator dots?