If like me, you've been to the filming of TG (MoD still own the land), then you would know who it was, unless u searched google of course. Ali is the daddy on this 1.
I believe the "Stig" is really Jeremy Clarksons' own personal milk fed gimp who has compromising photos of Jermey in a strange and ultimately blackmailable position. That's why he/she/it gets to blast around a track whilst Jermy salivates profusely over his sychophantic audience and producer.
Just my 2d's worth (that's 2 pennies to you youngsters)