In the days before the horseless carriage, the dashboard was a glorified plank of varnished timber or a heavy-duty leather apron that protected drivers from stones and mud thrown up by the horses. When equine quadrupeds were replaced by the internal combustion engine a century ago, the dashboard retained its function. But this was a function that grew in complexity and exponential fashion, so that today the "dash" is often an extraordinarily hi-tech, although hopefully understandable and readily useable, interface between driver and machine.

The dash tells us whether the engine is too hot or too cold, whether or not there is sufficient oil to keep moving parts adequately lubricated, how fast we are travelling, how much fuel is left and whether or not the engine is working too hard, or labouring, in any particular gear.

There was a real need for drivers to know all this, from the early days of motoring when engines were chronically unreliable to the days of fast and powerful cars before the advent of on-board computers. In most modern cars, however, all the driver really needs is a speedo, a fuel gauge and a small number of warning lights. In fact the dash can be, and ought to be, as simple as possible so that drivers can keep their eyes on the road rather than using them to scan banks of important looking but essentially redundant or irrelevant dials and switches.

Most modern cars don't need anything more complicated than the dashboard of the 1924 Leyland Trojan shown here. The Trojan, a primitive, cheap yet famously sturdy little car (adverts for the car asked "Can you afford to walk?") was so simple that it needed few instruments and it was so slow that a speedometer was pointless (speedos were not required by law until 1937). A Ford Fiesta or a Nissan Micra needs only one or two more instruments today.

However, here's the rub. Drivers, particularly those with Boy Racer genes, want lots of dials, instruments and switches to play with, whether or not these are important or necessary. While "Blower" Bentleys of the late Twenties really did need all those massive white-on-black dials and Bakelite switchgear, fast modern cars could easily do without them. But who would want a big, swish Jaguar without its trademark row of dials and switches? They are lovely to look at and make drivers feel important, as if they were at the controls of a Hawker Hunter or Concorde. Small wonder that, traditionally, Jaguar ads featured airline pilots striding purposefully from the cockpit of a big Bristol Britannia or fast Boeing 707 to that of an opulent Jaguar MkVIII or IX.

Yet whereas a Jag driver of the Fifties and Sixties did need the assistance of Smiths of England to drive with confidence, his successor wants the dials without needing them.

So, too, do people who cannot afford such powerful and luxurious cars. Which is why humble servants like today's Ford Escorts and Volkswagen Polos sport dashboards that look as if they could cope with the information pulsing back from a Nasa Space Shuttle.

In any case, the dashboard is the part of a car's interior that school children of all ages (and genders) look at first when judging the desireability and capability of a new or unfamiliar model. Speedos are studied assiduously and rev-counters scrutinised as embryonic Boy Racers tot up the number of dials and switches. Top cars will always have more than family hacks and post-driving test bangers.

More than exciting dials and switches alone, the dashboard is also an important statement of personal style. The best are works of art where engineering meets styling and fact balances fantasy.

There are those that are glorious pieces of Baroque cabinet-making (the Facel-Vega Albert Camus was killed in, for example, or any Rolls-Royce), those that ape the controls of Top Gun jets (Chevrolet Corvettes), those that promise Grand Prix thrills (TVRs) and those redolent of motoring in the Mr Toad tradition (Morgan, Bristol, Aston-Martin). And, there are those (Ford GT40, old Lotuses and MGs) designed to frighten passengers by placing the speedometer under their nose rather than the driver's blood-shot eyes (the effect of the 120mph slipstream, you understand, not alcohol).

Whether faced in walnut veneers, engine-turned aluminium, painted steel or grey plastic, the dashboard is the point where ambitions and dreams meet the addictive whirrings and mysterious workings of the car. Until drivers grow up (not a chance), the dashboard, in all its seductive irrelevance and padded out with stereos and airbags, is here to stay. And it still comes in handy when faced with loose chippings on the road.

Photographs of classic dashboards from 'Dashboards' by David Holland (Phaidon, pounds 24.99).

Leyland Trojan, 1924

The Trojan lived up to its name, a solid little family car that was about as cheap, as basic and as rugged as they came before the arrival of the Austin "Baby" 7 three years later and the pounds 100 Fords of the Thirties. The beautiful blue dashboard is almost entirely instrument and gadget free. No speedo (with a top speed of 42mph, who needed one?) Not even a fuel gauge. The lever on the right is a dipstick used to check the fuel level.

MG PA "Midget", 1934

The PA was a tiny and exquisitely designed mechanical terrier. It offered speed (nearly 75mph with the screen down) and, above all, sporting style at a knock-down price. The Art Deco dashboard makes a pronounced play of MG's famous octagon badge: dials and switches are encased in delightful chromed octagons. Definitely not ergonomic, the starter key and button are over by the passenger Oddly, the speedo and rev counter are combined in one delicious looking dial.

Chevrolet Corvette, 1955

The Corvette was the first real American sports car and the first production car to be made of glass-fibre. The kitsch Space Age dashboard is fun to look at, but it adopts a relentless symmetry that makes some of the dials all but redundant. Just look at that tiny rev counter... You can't see it? Nor could the driver. This is what you faced when you were cruisin' and playin' the radio with no particular place to go.

Ford Escort, 1995

The craze for fish-like organic design has clearly gone overboard in the gloopy-bloopy cabin of the latest Escort. Never has a cheap(ish) Ford been so laden down with such a comprehensive and bizarre looking dashboard. Yet is all this information and all these swirling plastic shapes necessary? Of course not, but they are there to make Escort drivers feel they have reached the BMW-Mercedes-Jaguar big league.

Nissan Micra, 1995

The Nissan Micra is one of the sanest and least pretentious small, contemporary cars. It has very few instruments because modern cars, for the most part, do not need them. This technological minimalism also encourages drivers to potter along gently as there are no whizzy dials to watch racing around to red lines and needle-stops. The quality of the plastic is exceptionally high. In effect, a return to the basic certainties of the 1924 Trojan.

BMW 3-series, 1995

BMW has designed the most consistently logical and ergonomic dashboards of almost any manufacturer over the past 20 years. The strict, functional look is styled in part to encourage drivers to feel they are at the control column of a jet fighter. Which they do when hurtling like the proverbial Hun out of the Sun on German autobahnen. But should we encourage this sort of behaviour in overcrowded, speed-limited Blighty?

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