Who would have believed it? The Prius brand is on the way to becoming bigger than Toyota?

I exaggerate, of course. Toyota is still one of the world’s biggest motoring marques, but Prius, the green model it created, is becoming huge.

It’s a marque within a marque. And while the main Prius model is a fine car for people who think green and want everyone to know it, it isn’t suitable for all.

Some need a bigger car. Fleet buyers and car hire firms want a people-carrier, so here we have the Prius+. It’s a seven-seater sub-100/km car whose statistics make astonishing reading.

The lower of the two available trim levels, T4, sits at 96g/km and is expected to take around 70 per cent of sales ahead of the 101g/km T Spirit tested here.

It’s similar to the mainstream Prius and it works in the same way. But the new model doesn’t quite use the same Hybrid Synergy Drive system as the five-seater, because in the latter the under-boot nickel metal hydride (NiMH) battery pack raises the load bay and means a third row of seats is not an option.

For the Prius+, the new and impressively compact lithium-ion (Li-Ion) battery has been cleverly sited in the console in the cabin, beneath the armrest.

This means the boot floor has been lowered and a third row of seats added to make the car altogether more conventional.

Of course, the roof line has been raised while trying to maintain a Prius shape, and there’s no doubting the practicality.

The middle row of three individual seats move backwards and forwards, firstly so that each of the occupants can get more shoulder room, but also so the space can be balanced between the two rows of rear seats.

It means that you can get seven 6ft people in the Prius+ which is staggering.

Nevertheless the practicality and intelligent management of space is thoroughly impressive, and families will find a lot to like.

The five rear seats, which fold flat and create a level load floor, have a brilliant one-hand-one-movement operation.

OK, so the boot lid is a little too heavy to be ideal, but it's something you can work around.

With all the seats up there’s 232 litres of space, which is pretty good for a people-carrier.

With the third row folded flat there’s a much more impressive 784 litres, which is more than enough for the vast majority of families.

Under the removable boot floor there’s a useful extra space for oddments. So, the Prius+ majors on practicality, but it does pretty well at in-town driving too.

One of the three selectable driving modes uses electric power only as much as possible, keeping urban emissions – and fuel costs – to a minimum.

The battery is small compared to that of a plug-in hybrid so its range in EV mode is only a few miles at best, but it’s surprising how well the Hybrid Synergy Drive makes that power last once you’re rolling.

Out of town, the car isn’t quite as successful.

The excellent ride quality from soft suspension means that handling isn’t its best point but in truth few people-carriers ride and handle impressively.

Equally, the constantly variable transmission (CVT) gearbox that gives smooth and quiet running at low speeds can allow the car to feel a little strained when accelerating.

But despite that, the ride is still very good and fuel economy at a motorway cruise is very impressive for what amounts to a 1.8-litre petrol car. As always for a Prius, it is crammed with kit. It features a rear-view camera, a panoramic roof, automatic windscreen wipers and a touchscreen infotainment system. For those who require a seven-seater car with excellent performance, hi-tech features and groundbreaking economy, it is a mouthwatering offer.