Up until now, beyond the price differential, one key reason to overlook buying a Mini - beyond its cartoonish design - was the lack of rear doors. And with sales in this market splitting roughly 65/35 in favour of 5-door models, it's clear Mini thinks that the core 3-door hatch's layout is excluding potential customers who buy into the Mini image and brand, but simply need more space, and more doors.

Sure, they could already buy a Countryman, but that's really quite a big jump in both size and price from the three door. Whereas the new 5-door Mini - in case you're struggling with scale - goes into battle with the Volkswagen Polo, Ford Fiesta and Audi A1 5-door. It's roughly the same size as each of those.

Compared to those cars, the 5-door Mini ticks all the boxes for interior space in a way the 3-door simply doesn't. Normal adults fit in the back. A buggy will go in the boot. And it makes a Mini a realistic daily car, even if you've got a small kid or regularly need to cart four people about - not something easily done with the 3-door.

Cartoon style not withstanding, the 5-door is immediately distinct - you're never going to confuse it for another brand. And the extra set of doors and larger rump help somewhat to balance out the new Mini's rather bulbous nose. The same idiosyncratic design signatures and interior architecture applies. It's just been photocopied up to 125 per cent.

Jump into the driver's seat of the 5-door and you could be in a 3-door, or any other Mini because the dashboard and layout is the same. Which means it feels like no other car on the road. And although it is an ergonomic shambles (you can't operate the centre screen controller with the armrest down) it all feels very bespoke.

Everything you operate has been "designed" - from the starter detonator switch, to the metal window rocker switches and the collar around the gear lever that flicks between eco, normal and sport modes, illuminating a coloured ring around that big centre dash circle.

"Maximum go-kart feel" the infotainment system glibly calls the sport mode. Yet for all this japery and layered design, the Mini 5-door still sings most strongly in the department it always has done - out on the road.

The steering is hefty, the ride firm - but in fact better than the 3-door thanks to the extra wheelbase length. The structure feels stiff and the car responds to your inputs with an eager, alert quality that speaks of extensive development.

The best bit is the engine. We drove the Cooper petrol most extensively and there's little need to pick anything else. This 1.5-litre, turbo-charged three-cylinder is part of BMW's new modular engine range, and it's a cracker. It's got the rorty thrum that's characteristic of a three-cylinder, which adds an unusual sonic edge to proceedings without getting annoying. And it pulls hard - really hard - from low revs, to the point that you'd swear it was a turbo-diesel in its torque delivery. But you can rev it out to beyond 6,000rpm and it feels quick. It makes you question why you'd bother with the Cooper S - because if you're gentle with it it'll clear 40mpg too.

Mini's making a big play of the tech features in its new generation cars, and the 5-door is no different. You get a skinned version of BMW's iDrive infotainment system - which in XL format (£1575) features the rotary control knob with touch-gesture functionality you get in BMWs - and apps, connected services and an enhanced Bluetooth system (which means you can connect more than one phone).

An 8.8-inch display screen sits like a letterbox in the middle of the centre-dash circle, which no longer contains a dinner-plate sized speedometer and no longer really makes any design sense. No matter, all the tech works just like BMW's iDrive too, which means it's really very good - you just need to get used to more lurid colours, cartoon-like graphics (spotting a theme) and reverse logic for scrolling which constantly wrong footed us.

The head-up display (£375 when bought with the Chilli pack) - big news in this small car sector - is not without its appeal, showing speed, turn-by-turn instructions and warnings on a small pop-up screen. Just be aware that this type of system - with the display on a secondary transparent screen, rather than project onto the windscreen itself - doesn't give you quite the fighter-pilot "everything in one focal range" vision that the car manufacturers would like you to believe.

Ultimately, it wouldn't be a Mini if you couldn't personalise it to death, and the 5-door gets the same treatment that the 3-door - choose your own style, colour and materials for body, stripes, wheels, roof, interior trim, lighting, and the list goes on.

But Mini is sensibly bundling a lot of stuff into packs now, and if you're buying one of these cars in the most obvious Cooper spec its make sense to add the £2250 Chilli pack because many of the options you'll want (bigger wheels, multi-function wheel, interior light pack, mini drive mode selector, nicer cabin materials) are included. And it makes others options cheaper, besides positively impacting on the resale value of the car down the line. Which means it's less of an expense than the headline price makes it appear.

That last line is a neat summary of this new 5-door Mini. On paper, the £15,990 starting price for a petrol Cooper 5-door, sounds expensive. A Pepper pack (Bluetooth, storage pack, climate control) is £890. But we'd go for the bigger, more expensive Chilli pack as mentioned. You also might want to consider Media XL (£1575) which gets you the 8.8-inch screen with full-fat navigation, touch controller and better Bluetooth. So a headline Mini 5-door will cost £20K. That compares to a Ford Fiesta, but that's hardly comparing apples with apples. You get more in the Mini - both kit and performance, and that's before you take into account the leading residual values and low CO2 figures, which make these cars cheap to run, attractive to finance and competitive as a company car.

Given that, if you're not as annoyed by the cartoon styling or bored of the same-as-before design theme, it's easy to see the appeal of Mini 5-door. It's not small any more. But increasingly the extension of the Mini brands is about making it accessible to people who need more than the standard 3-door car offers. And in many ways, the 5-door is now the best, and most sensible buy in Mini's extensive, seven-car range.