Some interesting info in this quote from another forum:
"The original R50/R52/R53 was a Rover design, BMW took it on when they split up the group, and switched all the tooling from Longbridge to Cowley. BMWs input was limited to the engine selection (Rover would have fitted the K Series), and a few quality enhancements. The R56 then felt rather rushed in 2006 – BMW had to get a new car out, and quickly. The Tritec engine was losing out massively to the competition in terms of economy, and certain bits of the car were expensive, and time consuming to produce – like the wrap around rear glass on the R50, and the clamshell bonnet. The R56 cut production times from 24 hours to 16 hours per car, and reduced the cost per unit, improving profitability, meaning BMW could invest more in the Plant Oxford infrastructure.
So this car is the first all BMW product. It's the first MINI hatch to have a 5-stud wheel pattern, the fuel filler moves from the LHS to the RHS, the exhaust config changes, the rear axle has been redesigned… it's a complete ground up new car."