SOMETIMES on a new car the bits you can't see are just as important as those you can.

The latest Ibiza from SEAT is a perfect example of the hidden world of what really matters in car design; the part that's counted in vast piles of pounds and euros to develop.

So, this new Ibiza from the arm of the VW Group that's finally making good on hopes for a profitable future is more than a stylish small family hatch.

For beneath the sharp suit sits (more or less) the same car that's coming at us in the months ahead as the new Audi A1, VW Polo and Skoda Fabia. SEAT's Spanish chest swells with the pride that they've got it first.

The new Ibiza is the fifth generation with that name and, with more than 5.4 million sold since 1984, comfortably the biggest selling model in SEAT's history.

The new one is going to have no problem swelling those sales figures as it takes on rivals like the new (and excellent) Ford Fiesta and still youthful Vauxhall Corsa. It might even rob sales from the forthcoming new small Audi A1, thinks SEAT.

Starting at £13,130, the new Ibiza comes only as a five-door hatch as demand for a three-door version of all small family cars continues to diminish. Current range topper is a new generously equipped XCELLENCE grade at £17,310.

There won't be an estate version, with SEAT's new small SUV Arona due in the winter to cater for those seeking extra space for people and things.

Like almost every new generation of car this latest Ibiza has gained in width (up 87mm) but is a mere 2mm longer and 1mm lower than before. Stretching front and rear wheels 60mm further part means a bit more room for rear seat passengers and boot space is usefully increased by 63 litres to 355 litres.

It's a fact rarely quoted that buyers of new cars are rather more mature in years than the marketing department likes to talk about - often into their fifties - but SEAT says its Ibizas buck that figure with the youngest buyers of any supermini, and 10 years more youthful than average.

To these mature eyes the new Ibiza looks a finely honed cracker, its sharply drawn lines making the least expensive model look a more sporty drive than the 75 horsepower engine beneath the bonnet can deliver. SEAT won't mind that at all.

All new Ibizas currently share varying versions of VW's 1.0 litre three-cylinder petrol engine, in 75, 95 and 115 horsepower trim and with five-speed manual gearboxes for all but the most powerful-engined FR version, which gets six speeds.

On the way is a diesel engine (1.6 litres and either 80 or 95 horsepower) and a seven-speed automatic gearbox option.

The least powerful Ibiza manages a gently lethargic 14.7 seconds to 62mph, a top speed of 104mph and average economy of 57.6mpg with 112g/km of CO2 from its tailpipe.

Things improve considerably with the 95 horsepower engine, surprisingly both on performance and economy and emissions. With a top speed of 113mph and 0-62mph in 10.9 seconds, the car is much more sprightly.

It also goes further on a gallon of unleaded - 60.1 miles officially, while putting out 106g/km of CO2. The most powerful (115 horsepower) engine manages an identical 60.1mpg but is quicker still (121mph, 9.3 seconds) and only a tiny bit more polluting, at 108g/km.

Standard kit on the entry level Ibiza S includes air conditioning, remote central locking, Bluetooth audio streaming, trip computer, 5ins monochrome touchscreen and electrically adjustable door mirrors.

Move to SE trim (from £14,000) and you add alloy wheels, front fog lights, colour touchscreen, leather wrapped steering wheel, gear knob and handbrake and split-folding rear seats.

The FR trim line (from £16,015 includes larger alloys, DAB radio, sports suspension, cruise control, front sports seats, dark tinted rear windows and 'FR' touches like a different rear bumper and flat bottomed steering wheel.

New XCELLENCE trim cars (from £16,715) include alcantara (mock suede) and pseudo leather trim, rear electric windows, rear view camera, dual zone climate control, parking sensors all round and auto wipers and self-dimming interior mirror.

Key options include a clear and easily programmed satellite navigation system for £660.

Whichever version you try there will be a similar feel inside the car, with well fitted but hard plastic trim and an approach to the world of driving that prizes clarity and ease of use over glitz - thank goodness.

The new and expensively developed underpinnings have produced a car that's both comfortable and, even without the most powerful engine, a delight to drive.

The car's 95 horses brought broad grins on a challenging Welsh hill route on the press drive and more smiles at the 60mpg recorded while going gently or the 45mpg when in full-grin mode.

Most people take a new car on a finance deal these days. A 95 horsepower Ibiza in SE trim (£14,965 OTR) will cost £186.64 a month over four years with a £1,459.50 deposit on a PCP deal. Looks like a bargain.