You really will have to be a committed Prius person to notice the differences between this Plug-in version and a conventional model, assuming of course that you miss the 'Plug-in Hybrid' logo on the front wing and the battery charger lid on the righthand rear wing. Other than that, it really is down to fine detailing - a larger lower front grille section with various chromed and silver highlights, a blue smoke paint finish in the extended sections of the upper headlamps, silver accents on the door handles and clear LED lamp lenses complimenting silver licence plate trim at the back.
Other than that, the changes made to this third generation Prius have been kept to a minimum. Including the major difference you might be expecting to find - that of bootspace. This Plug-in variant, after all, has a much larger battery than its conventional sibling and all those cells have to sit somewhere, taking up the cargo area as they did in early prototype versions of this car. But not in this final production version. True, the 4.4kWh Panasonic-developed lithium-ion unit raises the boot floor by a couple of inches, but that only takes two litres away from a luggage capacity that, at 443-litres - is very creditable indeed. That's 50% more than you'd get in a rival 'Extended Range Electric Vehicle' like a Vauxhall Ampera - or indeed something more conventional like a diesel-powered Ford Focus ECOnetic. If you need more space, pushing forward the split-folding rear bench frees up 1,120-litres.
There's more good news when it comes to the question of rear passenger space. For a start, don't take for granted the fact that you can - at a pinch - seat three people here. That's not possible in a rival Vauxhall Ampera or Chevrolet Volt, even though these are apparently bigger cars. There's also more room here - especially for the legs - than you'd find in something conventional like a Focus or a Golf and headroom is also adequate, despite the sloping roofline.
At the wheel, you're surrounded by Toyota's usual high standards of fit and finish, with the various switches and screens managing to easily impart an enormous amount of information very quickly. The dual-zone dashboard is exactly the same as that in the regular Prius, designed to minimise the time the driver has to spend looking away from the road.
You get an 'upper display zone' with a head-up display and a central meter cluster that includes the 'Eco Drive Support Monitor' from which so much of this Plug-in model's driving information can be gleaned. Further down is the so-called 'lower command zone', dominated by the 'Toyota Touch' multimedia screen situated next to the short, stubby dash-mounted auto gearbox shift lever that's positioned to fall nicely to hand.
Despite this Plug-in model's extra technology, it's proved to be remarkably trouble free. We came across a few owners who had problems with the infotainment touchscreen but other than that, there isn't much. The skinny tyres wear rather quickly and the regenerative brakes take a little getting used to, but otherwise, as long as you get a fully stamped up service history, you should be fine. Most examples should be very well looked after but some will have been used primarily as urban scoots (they neatly sidestep the London congestion charge) and as such may well bear the scars of life on the streets.
(approx based on a 2012 Prius Plug-in) Parts are relatively affordable. To give you some examples, you'd be looking at paying around £15 for a drive belt and either just above or just below £100 for an ignition coil, depending on the brand you choose. If the bonnet's damaged, you'll be able to get a replacement for just under £120; if it's the front wing you have to replace, it'll be about £90. A decent quality shock absorber will set you back about £150.
As many owners of the existing conventional Prius hybrid will know, the car doesn't go very far on battery power alone. It is great fun to waft around in virtual silence, but you only need to have gone a couple of miles down the road before the petrol engine thrums smoothly into life. This Prius Plug-in hybrid retains the usual Toyota Hybrid Synergy Drive powerplant, but thanks to smarter, rechargeable lithium-ion technology, it can, on electric power alone, cover longer distances - up to 15.5 miles - and reach higher speeds, the maximum in EV mode rising from 31 to 51mph.
In other words, you really can use this Plug-in model for much of the time as a proper electric car. Unlike an ordinary Prius, it's not just a petrol-powered hatch that uses batteries to occasionally help out and keep its running costs down. The difference of course is fundamental, offering up a car that can potentially run on cheap mains-generated electricity for most of the time, yet also one that doesn't induce uncomfortable 'range anxiety' when the time comes to venture further afield. That's important. While it's certainly the case that most typical journeys are very short, it's equally true that a very large number of car owners undertake longer trips several times a month. And no one wants to run the risk of getting stranded by the roadside.
In a Prius Plug-in, you won't be, even though you may have been trickling round on electric-only power all week. Of course, you could say the same of a rival model with so-called 'range extender' technology - something, for example, like a Vauxhall Ampera with its little petrol engine, there to help out when the batteries deplete. But then, that's a slightly bigger, slightly heavier and more expensive car. It's certainly a more complicated one. At first glance, the Plug-in hybrid concept does seem to offer a simpler approach.
Did I say 'simpler'? Well, as simple as any car can be when the concept behind it is this complicated. Let us try and boil down the essentials for you. The lithium-ion battery in this Prius Plug-in is different from the feebler old-tech nickel-metal-hydride unit in the conventional car, but all the other elements of the full-hybrid system are the same. Namely the 1.8-litre VVT-i petrol engine, the powerful electric motor and the generator, all driving through the same E-CVT automatic gearbox. The total power output's the same as an ordinary Prius too - 134bhp - though the extra 35kgs that's been added to the kerb weight (mainly due to the more powerful battery) means that the 0-62mph time is a second slower, occupying 11.4s on the way to 112mph. Not that any typical Prius people will be wanting to try and match these kinds of figures in practice. The soft ride, the vague power steering and the cornering bodyroll are all effective in discouraging an aggressive driving style in any case.
Anyway, in using this car, you'll have other things on your mind - not least the necessity of choosing between three different drive modes - 'HV', 'EV' and 'EV-City'. Most often, you'll select the 'HV' or 'Hybrid Vehicle' setting, which allows this car to work just as an ordinary Prius would, with the petrol engine constantly cutting in and out to assist the Hybrid Synergy Drive system as required. At any given time, a neat 'Energy Monitor' at the top of the dashboard shows you what is charging or being driven by what.
Now though, to the differences with this Plug-in model. If you select 'EV' (or 'Electric Vehicle') mode, the car will draw on the hybrid battery's full capacity for the 15 mile range and up to the 51mph maximum we mentioned earlier, provided that you don't use more than low to medium throttle. That's a big proviso in real world motoring, so much so that in tests, typical users told Toyota how frustrated they were by it, with the engine butting in all the time when the car was supposed to be in electric-only mode. So in response, the Japanese engineers have added a third 'EV-City' setting that allows more forceful use of the throttle before the engine cuts in.
If you can't trust yourself to be light-footed on the throttle pedal, selecting the 'Eco' setting that's operable in any of the three driving modes will restrict accelerator travel for you. That'll help you get the most from the electric-only driving range of course and the sensitivity of your right foot is something you can keep an eye on through the 'hybrid system indicator' that you'll find on the 'Eco Drive Support Monitor'. This gives you a bar graphic showing the point at which the engine will start under acceleration. Keep just below it and your silent progress period will be optimised, something further assisted by pulling the stubby little blue auto gearstick out of 'D' and into this lower 'B' slot. That'll encourage extra regenerative braking, reclaiming more of the energy that would normally be lost when you brake and using it to re-charge the battery.
Of course, no matter how careful you are, your electric-only driving range will be quickly used up, something you'll be able to keep an eye on via the 'EV driving range display' you'll find both on the 'Hybrid System Indicator' and the main 'Energy Monitor'. When the range depletes to zero, the car will seamlessly switch into petrol-electric 'HV' mode with hardly a murmur. And at the end of your journey, if you're interested, you can refer to a special 'EV Driving ratio' indicator that'll show you what proportion of it was covered on electric power alone. The display will also show you the amount of power and fuel used - and how much fuel was saved through using electricity from external charging.
Ah yes, external charging: we were getting to that. Using a provided five-metre cable that's stored in its own under boot floor compartment, the battery pack can be recharged in 90 minutes from a standard 230V domestic power supply - or from one of the many public charging points that are springing up in towns and cities all around the country.
Is this logical extension of hybrid technology the future of motoring? Probably not - but it's an important step along the way. It won't be very long before Plug-in technology is the preferred route for hybrid buyers.
But would you buy one of these on the used market? Well first of all, you'd have to find one: Prius Plug-in models are vanishingly rare. If you do come across one and you're a Prius fan, we think you'll like it. After all, if you want to run on electric power most of the time, yet need to have a conventional engine always on hand for longer trips, then this is one of the cheapest cars that can deliver exactly that. At a price which isn't much greater than that of a similarly equipped standard model Prius. So goes the argument for this car. It's still quite an expensive way to cement your automotive eco-credentials - but then new technology always is. If you get it though, you'll really bond with this car.