These are believed to be the first spy pictures of the BMW hydrogen hybrid technology undergoing testing.
The tech, revealed yesterday by autocar.co.uk, could be used by the next-generation Mini and the front-wheel-drive BMWs planned for 2014.
The system combines a conventional front-drive powertrain along with a hydrogen fuel cell, electricity-storing supercapacitors and an electrically driven rear axle.
As can be seen in these pictures, BMW engineers have already built functioning prototypes based on 1-series hatchbacks converted to front-wheel drive.
Company engineers say the “fuel cell hybrid technology” is designed to allow a vehicle to travel emissions-free in city centres, a feat beyond the ability of regular petrol-electric hybrids.
This drivetrain will fit into today’s Mini Clubman, making it likely that it could become an option for the front-wheel-drive BMW and Mini models that are at least four metres long.
The fuel-cell hybrid has not yet been given the green light by BMW bosses, however, and the firm has to be certain that sufficient sales would be generated to ensure financial viability.
It also needs to decide whether hydrogen fuel pumps will become available in most large cities.
The system works by having two independent methods of driving the car. In the prototype, a conventional transverse Mini drivetrain powers the front wheels. Mounted behind the engine is the Auxiliary Power Unit (APU), a slim fuel cell that develops just 5kW.