I doubt the tracking car would have been a Mini Moke, until quite recently a 2CV was always the vehicle of choice for camera tracking due to its unique suspension. I suppose a Moke would have been more able to keep up with the Coopers in the tunnel though.
According to Philip Wrestler the second-unit director who filmed the sequence and the stunt man Remy Julienne the camera car was a Mini Moke.
More on the sewer scenes...........
The Alfa Romeo police car crashing through the sewer gate contained dummies and was fired out the tunnel with the same rig used to blow the Minis out the back of the bus. The remote control used was fired by a film crew member disguised as a football supporter who is seen to run in and shut the gate just before the crash.
(Loads more detail on all this is in the book and dvd of the Making of the Italian Job by Matthew Field.)