Wouldn't be surprised if it's still Ben Collins. If the TG crew and he talked about it - why change The Stig? I mean he appeard as himself in the Dakar-thingy aswell. And "his times are very similar to the ones from the old Stig."
What's stopping them from using any old production crew as 'Stig' for these indoor shots, and using a driver for the actual driving? The marketing genius of the Stig is that you can use practically anybody, and it'll still be him.
This. Does the real Santa Claus have time to show up personally to a strip mall in Pewaukee, WI? Of course not. It would cost too much to keep him around for something so trivial, so they hire one of his helpers to stand in.