The accounts for BMW and MINI are handled directly by BMW in Munich in cooperation with various agencies across Europe - mainly in Germany though.
The ad you linked to was created in 2008 by draftfcb/Lowe Group in Zurich, Switzerland.
Other agencies that have done work for BMW AG and MINI across Europe are:
Aixsponza in Munich has done some visual work for BMW
Meiré und Meiré in Berlin and/or Cologne (they did the Roadster introduction in Detroit as well as the Mini iPad app and "The Mini International" magazine for example)
Interone in Hamburg created the www DOT defminirecords DOT com concept and webpage.
The annual reports for BMW (Mini included) are designed by abt-design in Munich
I also know that Hochkant Film in Munich did some stuff for Mini a while back.
And if I'm not completely wrong I seem to remember that BBDO and Saatchi & Saatchi were working on the BMW accounts for a while.
To be fair, Mini has such a tight and strict corporate design, it probably doesn't really matter who's doing what - BMW will have a very close eye on whatever leaves the building anyway.
[EDIT] I had links to all the agencies but the forum just kindly informed me that I'm only allowed to post links after I had more than 15 posts. So if you want to check out the pages, google the names