The MINI family keeps on growing, literally, with the Paceman.Motoring editor Andy Russell gives it a spin.

When you are on to a winner you make the most of it and MINI has proved to be an expert. Having started with a hatchback and convertible it has grown to an eight-model range with Clubman estate and Clubvan commercial, Coupe and Roadster and the bigger five-door Countryman has now been joined by the more dynamic, coupe-inspired three-door Paceman.

In keeping with the Countryman the Paceman offers more interior space than the 'standard' three-door hatch so aims to appeal to those who want to buy into the MINI brand or remain part of the family but need a bit more room.

Unlike the five-door Countryman which can seat five, the three-door Paceman seats only four with two individual, sculpted rear seats. Getting in and out of the back is easier than in the smaller hatch and, once in, adults have adequate legroom, provided those up front aren't greedy, but tall passengers will find headroom limited by that sloping roofline.

The boot is also more useful but the access narrows to accommodate the wide rear light clusters. It offers a useful 330 litres of spaces and is deep but the floor is oddly shaped – pay £200 for the optional luggage compartment package which includes a removable sill level floor panel. Rear seat backs split 50/50 to increase the load space to 1,080 litre but don't fold totally flat on to the cushions.

The fascia is pure MINI with the huge central speedo, eyeball air vents and the rev counter on the steering column. There are a lot of small buttons set low on the console but on they become easier to navigate with familiarity. What really threw me was the electric window switches on the Paceman moved to the doors rather than the toggle switches on the centre console – sorry to the person who sat behind me while I tried to get the window down to take a car park ticket.

The downside of the sloping roof, like a Range Rover Evoque, is a shallow back screen and small side windows so visibility is restricted and you're glad of parking sensors.

It shares engines with the rest of the range so a 122hp 1.6-litre petrol Cooper, 184hp 1.6-litre turbo petrol Cooper S, 112hp 1.6-litre turbo diesel Cooper D and 143hp 2.0-litre turbo diesel Cooper SD and 218hp 1.6-litre turbo petrol John Cooper Works. MINI's ALL4 all-wheel drive system is optional on all four Cooper models and standard on John Cooper Works.

I own a standard Cooper and whenever I test the S model wish I had the extra horsepower and livelier acceleration especially but I was disappointed by fuel economy of 35mpg overall.

But the biggest problem I have with the Countryman and Paceman is just that – to my mind, they are too big to be a true MINI but I know there are plenty of happy owners who will disagree.

As well as growing in size the Paceman feels more grown up to drive too. The ride is more composed so is more comfortable on long journeys but it's just not as much fun to drive. It handles well enough but the extra size has blunted its sharpness feel – it's lost some of MINI's 'go kart' fun factor and no gain in ride quality can make up for that loss.

The Paceman is not going to be a big seller like the more practical Countryman and it is unfortunate that the MINI family's new kid on the block came not long before the next-generation hatchback was revealed.

That too is a three-door that offers more space than its predecessor as well as getting the all-new generation of engines which is going to steer some of the attention away from the Paceman which has come on to the scene just a little too late. That said, the Paceman will be more exclusive which could be a big selling point with some people.