COWS with a conscience will soon be delighted to see soft spoken John arrive to milk them; as they push out global warming gases, his car doesn't even have an exhaust pipe.

For John, a man comfortably into his mature years, is one of the first Brits to buy a car that might just be the turning point for all-electric vehicles, transforming them from hair shirt transport for eco warriors into something you'd sell the Aston for.

John, who lives in Cornwall, was so delighted with the prospect of his imminent Tesla Model S delivery he trained it to Birmingham to see an electric charging point officially opened. That's dedication to the cause.

He is, incredibly, moving into the £68,700 Tesla from... a well used Citroen diesel. Because the new car, worth many times his current transport, will cost a lot less to run.

And he'll be up at 4am every day to whisk the Tesla over to the farms where he acts as what the dairy industry calls a relief milker; someone who gives the farmer the chance to take a holiday.

Not, you suspect, a common buyer's profile for this big, expensive (but cheap to run) car with Aston Martin looks from a company chaired by a chap called Elon Musk, who co-founded internet payments via PayPal and whose current interests include building successors to the NASA Space Shuttle.

He is obviously a busy man (did I mention his interest in an air travel machine that would manage a 350 miles journey in half an hour?) and wasn't at the Hyatt Regency Hotel in Birmingham for the ribbon cutting on the second Supercharger site in the UK (the first is at the Hyatt Regency Churchill hotel in London), where Tesla owners can rapidly recharge their cars for nothing.

Most owners will be happy with a £5 overnight charge at home and the more than 300 miles range a full set of batteries will give them, but it's good to know you needn't be stranded, especially as the Supercharger network expands across the country (and world, as it happens; Musk is a man with a big vision).

What of the car itself? Well, relief milker John has a startling surprise in store. His single test drive saw him reach the heights of 40mph; his first proper press of the accelerator will shock him.

This is a car that makes a passenger shriek (my ears were witness) at the way it kicks for the horizon when provoked.

That's after rolling near noiselessly out of London on its way to the Birmingham plug in ceremony, with only the odd thump as a big, heavy wheel and tyre bumped into a pothole or two.

On the motorway the progress is punctuated by unnecessary prods of the throttle for the extraordinary punch in the back that provides ('it's addictive' someone says afterwards), although tyre roar at speed makes the Tesla Model S no quieter than its conventionally powered opposition.

Which might include a four-door Aston Martin Rapide, except that would cost £53,000 more than the Tesla, drink petrol like a parched tippler and present vastly less rear passenger room and luggage space than the new arrival from the States.

Or perhaps you might fancy the fastest Range Rover, whose big petrol engine makes it accelerate only a little less quickly than the heavy (but still lighter than a RR) Tesla and which enjoys only a little more boot space, while pumping our carbon dioxide like there's no tomorrow. A bit thirsty too and nearly £30,000 more than the Model S.

Of course, the Tesla's electricity has to be produced somewhere, perhaps at a coal fired powerplant which is filling the atmosphere with global warming gases. But it might be coming too from cleaner sources (like nuclear) and it isn't adding to the dirty air in cities, where so many of us live.

There are three versions of the Tesla S, starting from £49,900 for a car with smaller batteries (for up to 240 miles a charge) and less performance than the top P85 driven here, and which will also need another £1,800 spending to use Supercharger sites, a feature built into the other versions.

All share a fabulous interior dominated by a vast 17ins touchscreen that spent the day displaying a detailed map of our route that twice said we'd entered a one-way street and needed to turn round, when we were scything our way along the M1.

So nothing on wheels is perfect. But the Tesla Model S comes close to an ideal vision for the future of motoring, and a cheaper (from perhaps £27,000) saloon is on the way to challenge the BMW 3 Series for more affordable cool.

£68,700

410 bhp electric motor driving rear wheels via single speed gearbox

130 mph

4.2 secs

50

Up to 312 miles per charge

0 g/km

0%

4yrs/50,000 miles (battery eight years unlimited miles)