If you saw a button labelled "Sport" on the dashboard of an unfamiliar car, you'd push it, wouldn't you? Let's say you were 10 years old and sitting in the passenger seat. You'd think: "Sport. What the hell does that do?" And then you'd push it.

Here's what it does: it temporarily transforms a trim but otherwise sensible-looking three-door Astra into a rapacious, road-eating beast. More specifically, it changes the throttle response to give "crisper initial acceleration". This comes as a bit of a shock when you've just put your foot down in the hopes of traversing a busy junction before the lights change. The purring of the engine rose an octave, and the minivan in front of me was suddenly rendered in extreme close-up. "Don't do that again," I said.

But curiosity got the better of me and, a few hundred yards later, I was telling him to do it again. "This time wait till we hit the bend, then engage." The Sport button, it transpires, also makes the steering more responsive, but it's hard to judge the precise difference unless you're veering about maniacally as you switch it on, and it's difficult to find roads where this sort of thing is tolerated. While it provided us with a fair few minutes of entertainment, I must confess I do not see the point of this facility. Looked at another way, this is a button that gives you a burst of sluggishness and muddy steering whenever you turn it off. If one mode is demonstrably better than the other, why have a button in the first place?

The idea, it seems, is to give people the option of driving according to one's mood. To my mind, mood ought to be less of a consideration when choosing a driving style than, say, weather conditions. Allowing people to select a distinct automotive "feel" without switching vehicles ("Here, just press the dune buggy button! Or try this one: sledge!") simply contributes to the dangerous and already pervasive delusion that driving is some kind of virtual experience unconnected with a large hunk of metal moving at speed. If nothing else, they should put the button in the boot, so you can't keep changing your mind.

In many ways, the Astra Sport Hatch is neither fish nor fowl, but this is not necessarily the result of compromise. This is not the basic, one-up-from-the-house-white vehicle it still resembles from certain angles. Nor is it simply a compacted, low-slung version of its dowdier cousins, the Astra Life, the Astra Design and the Astra, erm, Expression. It's got plenty of power and the ability to control it. It is a car that exudes a quiet confidence, or when in Sport mode, a slightly louder confidence. It is difficult to summon up an image of the typical Astra Sport Hatch owner - perhaps neither quite fish nor fowl himself - but if this car could hold its own on a test track, it also wouldn't look out of place stopped in a lay-by for a nice cup of tea and a few sandwiches. The interior is very comfortable. You wouldn't even need to stretch your legs.

In this sense, it may be the perfect car for me. Although I frequent neither test tracks nor lay-bys, these days I sometimes find myself fantasising about both. If the phrase "Sport Hatch" puts one in mind of an overgrown boy racer, the words "Vauxhall" and "Astra" remain firmly associated with the sort of old-fashioned pragmatism I'm beginning to find deeply attractive. Even as I zipped through traffic listening to the stern voice of the satellite navigation woman (she was constantly attempting to direct me to the home of the car's previous driver; I couldn't figure out how to shut her up), my chief thought was: "I'm in a Vauxhall! If I crash think how inexpensive the repairs will be!" I was thrilled by the news that the company has introduced a cheaper way to replace windscreens and that parts of the headlamp unit may be replaced individually. I imagined nipping down to the dealership to have the electric wing mirrors reattached for a wholly reasonable price, rather than having to stick them back on with packing tape, as I've done on my own car.

In the end, I did not get to test the Astra's eminent reparability, nor did I have need of its comprehensive array of airbags. The local vandals left its wing mirrors alone. I barely got a chance to admire its comparative parsimony with petrol, or fill up its capacious boot. Instead, I put it into sport mode and gunned off to strange places - the sort of anonymous, leafy places I imagined Astra owners called home. Then I set the steering back to vanilla and let the SatNav woman guide me home (my son eventually mastered the system, but he couldn't work out how to make her sound less patronising). It seems you really can have it both ways with your Astra. Just not at the same time. Giles Smith is away.

The lowdown
Vauxhall Astra Sport Hatch SRi 2.0 Turbo

Price: £17,875 (range from £14,175)
Top speed: 136mph
Acceleration: 0-60mph in 7.9 secs
Consumption: 31.4mpg (combined)
At the wheel: A beatnik accountant
On the stereo: A woman telling you to turn left at the next roundabout
En route for: A country gastropub with valet parking