Desperate to drive into a lake? You'll be after a Gibbs Aquada, then. It's the world's first factory-produced, customer-ready, high-speed amphibian (or HSA) and represents a one-stop shop for all your car-dunking needs. True, you can get amphibious vehicles in kit form. And the military might be prepared to sell you something they've finished with. But they won't do 35mph across water and come with a stereo. And, in the case of the military vehicle, it may have had several hundred not particularly careful previous owners.

Maybe you saw an Aquada in the papers recently when Richard Branson piloted a slightly reinforced, carefully branded one across the channel. Or perhaps one cut you up recently while you were water-skiing. Either way, the car is hard to miss. On land, it looks like a large sports car that has recently run over a boat. On water, it looks like a large boat that has recently run over a sports car.

One afternoon last week I drove an Aquada on a series of standard road surfaces in Warwickshire, where it behaved exactly like a car. Then I plunged it into a lake near the Gibbs factory in Nuneaton, at which point it started acting like a speedboat - a speedboat powerful enough, moreover, to pull a water-skier. And at no point during its transition from one to the other was I required to leave my seat or, indeed, do anything more strenuous than arch my eyebrow and press a solitary rocker switch to the left of the steering wheel.

There's no leaning over the side to haul in sheets and ropes, then. There is, in fact, no nautical business whatsoever. You simply ease the car into the wet and push the button. At which point, 10 years of work by Gibbs, involving the patenting of 60 new pieces of engineering, springs to life, causing the wheels to uncouple from the drive shaft and pivot up under the car's body, roughly in the manner of Chitty Chitty Bang Bang.

And when, seconds later, the light comes on to signal that the wheels are stowed, you are directly free to put your foot back on the pedal and resume your journey, only this time with a fetching plume of froth behind you. Ahoy there, indeed.

Given the precedent set by chase scenes in countless blockbusting movies, it could prove tempting to take the car up to 80mph and burst off the end of a jetty, preferably with an exploding warehouse in the background. But for now, I'm afraid, the Aquada works best when given unhassled access to a gentle slipway.

In any case, nosing the car on to a lakebound slope is a powerfully counterintuitive maneouvre which it proves hard to feel gung-ho about. Driving head first into water is so much the opposite of what you are taught to do by the people at BSM that you find yourself wrestling with your better judgment, right until the ectsatic moment when you feel the car adrift on the current and realise that it isn't going to sink like a box of rocks.

Give the engine (a V6 from a Land Rover) enough revs, and you are soon skipping across the surface like a pebble and thudding heartily over the wash created by nearby wake-boarders, passing car containers and so forth. You can also pull some pretty fancy, rapid full-lock turns, to impress or irritate other water users. (Gibbs say they have never flipped one on the water, try as they might.) And when you've had enough, you merely approach the slipway, press the button, idle awhile, and then emerge with the car's bodywork, but not your own, dripping.

There are hints, in the shape of that body, of a Mazda MX5 or MGF, with which the Aquada appears to share a studded aluminium petrol cap. Except that the Aquada is three seats wide, with the driver (or captain, as we should probably call him) occupying the centre, and the passengers slightly astern to port and starboard.

Also, unlike your average sports model, the Aquada has no side or rear windows. Nor does it have any doorhandles, which turns out, on closer inspection, to be a direct consequence of its having no doors. You climb in over the sides, giving yourself a leg-up on the running board.

The cockpit that confronts you is no different in feel from that of any regular automatic saloon car, except in having a greater than average provision of water-friendly fabrics. And I suppose no regular car that I know of comes with bilge pumps as standard, though given the amount of semi-liquid detritus flushing about on the floor of the average family vehicle, they might as well.

All things considered, it may be possible to have more fun in a car than this, but I'm not sure how. One is aware, of course, that, at £75,000, the Aquada is more of a rich person's plaything than a sensible solution to transport problems for island-dwellers. That said, Gibbs at one stage thought they were going to have to charge £150,000 for the Aquada. So you could say it is already half price. Bargain! And think of what you'll save on ferry tickets.