Super-green vehicles are here, having taken off in the US thanks to enormous savings in fuel costs and a vastly improved range – but are they worth the sky-high prices?

Climb behind the wheel, hit the "power" button and a host of lights on the dashboard leap into life. The car's range in electric mode, you immediately learn, is 50 miles, plus a further 310 in petrol-powered reserve. You shift the automatic lever into drive, and it moves silently out into the traffic. The lack of any engine noise apart, this car goes like any other executive car – albeit with a slightly smaller interior than most. Welcome to the Vauxhall Ampera, hailed by its fans as the first "e-car" that, crucially, has the range to take you any place you care to go.

This week Guardian Money examines the host of super-green cars to hit UK showrooms in the past few months and assesses whether they are now a serious alternative to conventional cars or remain rich people's toys.

The petrol savings are eye-watering. Charging an Ampera to go 50 miles will set you back around £2.50–£3, or nothing at all if you can access council-installed charging posts. Unlike other electric cars, this one has a petrol engine that will keep the wheels turning after the charge runs out. There's no vehicle tax or congestion charge to pay. But the purchase cost is very high; £30,000 after the government's £5,000 grant still makes it twice the price of the cheapest Ford Focus or £10,000 more than a standard Ford Mondeo. The hours spent recharging will also put many people off. Overall, our analysis suggests that while the Ampera can, for some drivers, deliver financial gains, most average motorists will find that a Toyota Yaris hybrid, at under £15,000, is a more realistic option.

The Ampera – voted UK Car of the Year 2012 – was launched in the United States as the Chevvy Volt, and sales initially tanked, delighting right-wing commentators who derided it as the "Obama-car". But more recently, especially in California, sales have begun rising, although sales of other electric cars, such as the Nissan Leaf have been miserable.

Will e-cars catch on in the UK? Money did the number-crunching and found that someone currently driving a 35mpg petrol car 80 miles every working day (around 20,000 miles a year) should save around £3,000 a year in petrol by switching to an Ampera – but, crucially, they will need somewhere to charge the car at work and at home.

Anyone living in a flat, or even a terraced house without a drive, will find it impractical to charge up the car unless they live in areas such as Brighton, Birmingham and large parts of London, where free charging posts are now relatively common (they are even popping up at motorway service stations). Run the car for a decade, though you will easily make enough savings on petrol to justify the initial price tag.

The alternative is to buy a hybrid (petrol/electric) car, available for less than £15,000 – not much more than it costs to buy a new standard diesel model.

"Range anxiety" has long been the issue (after price) that deters buyers. The all-electric Nissan Leaf can only cover 90 miles before a recharge, and then it's not like filling up at a petrol station – it will take four hours or more. This is Ampera's trump card, as it can be driven on as an electric-only car – for the cost of just a few pounds in electricity – and still be taken on a 300-mile trip with the help of its petrol back-up.

If you're wondering why the Ampera qualifies as an electric car rather than a hybrid it's because the Ampera is always powered electrically. Its 1.4-litre petrol engine only comes life when the battery becomes depleted, feeding enough power back to the battery to keep the car going.

Crucially, it's the electric engine only that drives the car. In a hybrid, the petrol engine drives the car above certain low speeds.

Vehicle renting company Zipcar, one of the first major buyers of the Ampera, offered us a test drive, and we were genuinely impressed. What strikes you first is that, unlike some other electric cars, the American-built Ampera has an executive, well put-together feel, and its relaxed drive is well suited to urban motoring.

Put the car in "normal" driving mode, and it does the rest. On a four-hour, high-power, charge – or six hours plugged to a household socket – it will go almost 50 miles of normal driving in electric mode before the petrol engine helps out.

Officially, the Ampera offers 235.4mpg, but in theory, if you drive 40 miles to work, give it a full charge, then drive home, you won't use a drop of petrol. Meanwhile, every time you brake, the energy is recycled to recharge the battery.

Inside the four-door car the battery takes up some room. As a result the interior is smaller than you might expect – similar to a compact exec car. There are two rear seats which would be OK for children, but accommodating two Olympic hammer throwers would be struggle. The rear visibility isn't great, but there is a reversing camera in the dash, along with a very swish satnav. The hatchback boot space is small for a car of this size, but not absurdly so.

Contrary to what many people think about electric cars, the acceleration is great. Vauxhall says 0-60mph is achieved in nine seconds and the car will go up to a top speed of 100mph. Running in petrol-generating mode the car appears to return around 40mpg, until it can be recharged.

The Ampera is backed by a "lifetime/100,000 mile new vehicle warranty", while the battery system has an eight-year/100,000 mile warranty, transferable to subsequent owners. Servicing is annual, at one of the 24 dealers supplying this car in the UK. Insurance is likely to be the same or a little higher than comparable-sized conventional cars. Reliability and battery life remain the big unknowns, as are likely resale values (though Zipcar says early signs are encouraging). The 100,000- mile warranty should ease some buyers' fears, but to pay out £30,000 on such a car is still something of a leap of faith.

Ultimately, the price tag is likely to put off all but the most committed of buyers. However, if you drive to work and have access to recharging points, it's worth trying an Ampera and seeing if the sums work for you, particularly if you pay company car tax. A stress-free option could be to lease one. Contracts can be had from around £400 a month, which sounds a lot until you realise your fuel bills could be a fraction of what they are now.

The Mini E – is this the future of eco-friendly driving?

Whoosh: Mark King and the BMW Mini E. Photograph: Katia King

I've never turned heads driving a 10-year-old Volkswagen Golf, but pootling along the residential streets near my Sussex home in a prototype Mini E seemed to attract admiring stares from pedestrians. Perhaps they were as fascinated as I was by the eerie Star Trek whooshing noise the car makes.

BMW has taken an existing Mini shell and retro-fitted it with battery power to create the Mini E, a fully electric vehicle. When it arrived on my doorstep – a loan from EDF Energy – one major drawback was immediately obvious: it requires so many batteries to power it that there is no back seat. For a family of three this makes the Mini E somewhat impractical; it's for one driver and a single passenger.

At least as it gave me a chance to see how the car handles – and boy, does it handle well. With instant acceleration, there's no delay between touching the pedal and moving forward. Touch it too hard and you're thrown back in your seat. It's fast. Really fast.

The speedometer indicated the car might be able to reach speeds of up to 160mph, though I was told BMW had capped my vehicle at 95mph. When I ventured on to the A23 near Brighton, I (safely) floored it and discovered the car had no problems reaching a legal 70mph. It kicks myths about electric cars being like milk floats firmly into touch.

But a feature known as "regenerative braking" was hard to get used to. In order to put juice back into the battery, and prolong the range of the car, it brakes of its own accord the second you lift your foot off the accelerator. When approaching junctions this can be useful, but if you're used to gently easing off the accelerator and cruising slowly to a natural stop it's disconcerting at best and irritating at worst.

Speed-freaks might be frustrated too. The faster you go, the more charge you use up, and there are far fewer charging points than petrol stations. In some ways this makes it safer for other road users and pedestrians because it encourages slower, responsible driving, although the car's near-silence means you might worry that pedestrians can't hear you approaching.

Clearly, it's that all-important range that is the big question. The Mini E I tested was locked to accept only a 12-volt charge, which meant it took eight hours to fully charge the battery (a 30-volt charge would halve this time). And for your eight hours you get about 100 to 110 miles, making it only really practical for someone who can charge it at home – but this requires a piece of kit costing around £800 to ensure your mains electricity is safe. Without home-charging, you'll quickly develop "range anxiety" – constantly worrying about how much juice you have left.

There are plenty of electric car charging points in Brighton and I had no trouble finding one; most are free to use at the moment. While I knew I wouldn't be giving it a full charge (I didn't fancy hanging around for eight hours), I had to laugh when I looked up at the sign that read: "Max stay three hours" – that wouldn't get me half-charged let alone fully topped up. To be fair, that's an issue for the local council rather than BMW or Mini, but it does make you wonder how councils will cope if electric vehicles do take off. Will all public charging spaces become ridiculously busy? Will councils introduce fees for using them? Will they build more to cope with demand?

The estimated 3p a mile running cost would more than halve my current expenditure, but the range of the car and the tiny interior makes it impractical for my family, and if you do wish to drive far, you'd have to make repeated stops to boost your battery.

If you're single, in a couple or run a city-based business, it'll be much more appealing, but even then a fully electric car will be no good if you live in an block of flats or do not have a garage, driveway or parking spot near your property. Mark King