Fisker Automotive, has revealed the next chapter in its quest to move from a start-up producer of swoopy supercars into a mainstream manufacturer.

Called the Atlantic, the stunning all-new four-door saloon developed under the codename of Nina will go head to head with the BMW 5 Series and Audi A6 when it goes on sale ‘sometime in 2013’. It will cost around £40,000 after tax rebates, according to the company.

Powered by a similar electric drivetrain with petrol engined generator set up as the Karma, the Atlantic ditches the occasionally rough-edged GM-sourced four-cylinder turbo in favour of a shiny, new 240bhp/260lbft BMW unit. Codenamed the N20, the slick twin-turbo engine will be also be used by BMW in the entry level Z4, 328i and 528i.

No official details have yet been released about the Atlantic’s chassis, but the company has confirmed that the car will be offered in both rear-wheel drive and four-wheel drive layouts. Performance versions echoing BMW’s M Sport models will be added to the range after launch, as will a convertible.

The Atlantic’s production debut will be followed by the launch of the Fisker Surf sportbreak, but no date has yet been set for the Karma’s convertible cousin, the Sunset.