From
http://www.preromanbritain.com/gwem/...00/history.htm
The car had a complex (in what it did) yet simple (in the way it went about it) transmission from FF developments. It had 3 different torque splits: fully rear wheel drive (for fast tarmac stages), 63:37 (rear bias for multi purpose use), and 50:50 (for when the going got tough). The torque split could be selected on the move, ie without stopping. However this feature was disabled on many road cars. The car also had three viscous couplings to put the power down where it was needed.
I'm guessing the small shifter adjusts either the viscous couplings or the torque split.