It was designed by Rover and then rebadged as an MG! 
It's not just a rebadge though, there are a load of differences and infact it was styled by Rover but a lot of the fit and finish and engineering design is BMW. It has a BMW engine and BMW Z axel rear suspension. Not to mention over the 75 it has a different spring and damper rates as well as all the subframes and steering rack being solid mounted with cast ali pieces replacing the rubber mounts. Driving a ZT vs 75 is night and day. One's a wafter the other a sports tourer.
But hey keep the bashing coming, I'd rather have 2K in my back pocket than drive something with VW or Audi badge just to keep up with the joneses. I already have my fun cars, this is just the work hack and why would I want to pay more for something I didn't even really want?
Nick