It's the new base because TopGear used to be in 30 mins formats, every thursday at 8pm for the series...
It was Quentin Wilson and Jeremy Clarkson were the main presenters, and the likes of Tiff Needell and Vicky butler Henderson and the likes presented for a while and then left, eventually forming, as you know, Fifth Gear.
I believe that the 30 mins format ended in 1998 possibly? and then Jeremy Clarkson bought the rights to TopGear and decided to bring it back, and that is when the 1 hour format was created.
Gota love TopGear
