The fourth part of BMW’s 1-series family has been spotted testing in Norway. The 1-series coupé, a two-door notchback version of the firm’s successful hatch, is the final part of a line-up that includes the current three- and five-door models, and the forthcoming convertible.BMW's two-door One has been designed primarily for the American market. Americans are known to be no great fans of any hatchback, no matter how upmarket. VW's four-door Jetta V6 always far outsold the equivalent Golf there, because US customers, very much like those in the far east, attach greater desirability to 'sedans' than hatchbacks. The addition of the 1-series Coupe, therefore, will coincide with the model's introduction in North America, where the lion's share of global sales are likely to be generated, and where it'll be pitched just above Toyota's Scion TC and Honda's Civic Coupe.The coupe's model range is likely to be made up for 116i, 120i and 130i petrol iterations to begin with, as well as a Europe-only 120d oil-burner. There are two options for performance versions of the car. The highly-tuned 170bhp 2.0-litre four-cylinder engine from the 320si could be added to the range, creating a successor to the original E30 M3, and a natural rival for hot hatches such as the Golf GTi and Focus ST. Higher up the range, Munich could also shoehorn its lightweight, twin-turbocharged 3.0-litre six into the 1-series coupe, creating a 300bhp, £30,000 1-series coupe, and an attractive alternative to a Nissan 350Z or a Porsche Cayman. Autocar's sources suggest the latter is the most likely course of action, since the coupe's structure will be inherently stiffer than a hatchback’s, making it the perfect basis for the ultimate M-division 1-series. They're split, however, on whether it will be called 'M1' or just '135i M-Sport'; the latter name may be preferred to better differentiate the car from the M1 supercar of 1978, which remains the marque's only mid-engined car nearly 30 years after it was introduced.