No way we could get 2 seats in our small 1-Series. While it's fine for my wife when in the passenger seat with the child seat behind her, the drivers seat would be far to forward if we were try to and fit one behind me.
If you're talking about the BMW 1-Series this has a peculiarity that most small cars don't have: a rear wheel drive (or all-wheel in some models) and a longitudinal mounted engine. This means substantially less space inside, especially in the back with the higher floor and the drive shaft down the middle. I found the Polo a lot more spacious than that.
