The BMW i3 platform will be stretched to create a new family car probably called the i5, according to insiders.

The new model would be notably more family friendly, with extra legroom in the rear cabin and a bigger boot. BMW admits that it has already trademarked the monikers i1 through to i8, making it clear that it intends to expand its new ‘i’ sub-brand.

The i3 is just four metres long and Autocar understands that BMW engineers think that by adding just 100mm of extra legroom and another 150mm of rear overhang, they can create a spacious family EV hardly longer than a Mini Countryman.

Creating the i5 is potentially a much cheaper and simpler operation than stretching a conventional steel monocoque car, as the i3 uses a separate chassis. Lengthening it is mostly a matter of extending the chassis’s longitudinal aluminium extrusions.

Likewise, because the body is made of carbon fibre-reinforced plastics, extending the pillarless passenger cell is mainly a case of stretching the roof and floor sections. Only the rear door structure would have to be completely re-engineered, although the hinge and clamp systems would be unchanged.

It’s not clear yet whether the i5 would need a more powerful range extender unit because of the car’s greater load-carrying capability. The model is unlikely to appear before mid-2015.