I believe they've also used other SUVs on a few occasions, cars which were being used on the "Loaners" (long term tests) section of Top Gear magazine.
The "making of" of Clarkson's last few DVDs which uses most of the crew and equipment of Top Gear, is available from the FTPs. You can see the chase cars in action - and in the metal - there.Yeah and sometimes an Audi A3.
There's a production company in the US that uses an Evo 9 as a chase car. Maybe they use something similar