Sometimes choosing a diesel car comes down to simple arithmetic. You work out how much more the diesel option is over the equivalent petrol car, calculate how many miles you're likely to drive the car in your ownership period and then figure out if the diesel premium is worth it. That presupposes two things. Firstly, that the petrol and diesel models are equally attractive to drive and secondly, that the manufacturer has been helpful enough to make direct comparisons possible. With their Clio III, Renault have been agreeably transparent and the cost to the customer is around £1,000.

On an executive car, this premium would be mere bagatelle. Not only would it represent a smaller proportion of the overall cost, but given that bigger cars tend to cover bigger mileages, you'd recoup the difference back rather quickly. With the Clio, it's not such a cut and dried deal. Take the entry level versions as an example. In Extreme trim, the 75bhp 1.2-litre petrol three-door Clio costs £9,165. Choose the 68bhp 1.5dCi diesel engine and you'll need to fork out £10,315. But how many miles would you need to drive before the diesel car paid for itself? If you drive 10,000 miles per year and keep the car for three years, it's not even close. Taking into account the car's fuel consumption and the difference in price between petrol and diesel fuels, the 1.5dCi version will save you £486 in fuel over that three year ownership period. In other words, you'll need to keep the car for twice as long as that to see a saving solely as a result of fuel bills.

"With three variations on the 1.5dCi diesel theme, Renault are hoping to cover their bases in a cost-effective manner"

There are other attractions that swing the balance back towards the diesels. There's not too much difference in residual values so we can leave that one alone. Company car user choosers will prefer the diesels for the benefit-in-kind saving they'll make but private buyers will often prefer them for their sheer ease of use. Let's look at the entry level cars again. The 1.2-litre petrol manages to generate 77lb/ft of torque whereas the starter diesel is vastly superior at 118lb/ft. This means that in typical urban/suburban driving, the diesel car pulls away more cleanly, feeling stronger and sprightlier off the mark. It'll also have an easier time merging with faster traffic on main roads. Then you've got the added convenience of a much bigger range to factor in. If I could cut my petrol station visits by a third, I'd probably also cut my consumption of crisps, fizzy drinks and chocolate bars by a corresponding amount!

Renault bring three versions of the 1.5-litre dCi diesel engine to the Clio III. First up is that 68bhp entry level model, available in Extreme and Expression trims. The middle child is an 86bhp version of that unit that sees action in Dynamique and sporty Dynamique S trims. The range-topping 106bhp powerplant is reserved for Dynamique S and Initiale variants, with prices topping out at £16,000 for a five-door Initiale fitted with a six-speed gearbox. More representative, for UK buyers at least, will be a solid mid-range like the three-door Expression dCi 68, priced at £10,915. For a premium of around £900, you can opt for the Sport Tourer estate version with the 86 and 106bhp engines, this variant offering around 50% more luggage space.

These prices look competitive compared with rivals and although they are a little higher, model for model, compared with the old second generation Clio, which continues as a new car in slightly cheaper five-door 'Campus' form but with the older dCi 65 engine. We'd go for the more modern Clio design. It's not that much more expensive and not only are you getting a more up to date engine but it's also worth remembering that the Clio III's increased safety and security means that it's in a lower insurance group than the older car. Over a typical three year ownership period, this will make it cheaper to run.

Let's take a look at a few of those standout safety functions in a little more detail. The Clio III has excellent neutral weight distribution and some serious brakes to prevent an accident happening in the first instance. It is delivered as standard with Generation 8 Bosch ABS plus electronic brake force distribution (EBD) and emergency brake assist (EBA). Other options include electronic stability programme (ESP) incorporating ASR traction control, understeer control and MSR engine torque overrun regulation.

Along with the Modus, the Clio III was the first car in its segment to offer additional beam cornering headlamps, while double distance xenon headlamps are also available for enhanced night visibility. The Clio III's structure includes a number of programmed deformation zones and has been designed to function with Renault's third-generation System for Restraint and Protection. This includes up to eight airbags, incorporating two adaptive front airbags complete with load limiter and double pretensioners for the front seats. If you must crash, at least have the foresight to do it in a Clio III.

Comfortably bigger than the outgoing model, Renault have now been able to take a leaf out of General Motors' book and allow the utility models (like the Modus) to concentrate on family duties, freeing the Clio up - as Vauxhall has done with its Astra - to be a bit sassier than before. Therefore the lines are sharper and sleeker than the rather bulbous previous two generations and there's greater production emphasis on the sportier three-door model, a car which is expected to account for over 75 per cent of UK sales.

The Renault Clio III offers a more sensible and cerebral package than its predecessor, ruthlessly targeting the key supermini buying criteria. That's why the diesel models will prove so popular. It remains a car that you'll buy with your head rather than your heart but on any objective basis, the latest Clio diesels more than measure up.

TOP 5 CLIO DEALS

The results below show the top CLIO deals on buyacar

	Renault Clio 1.5 dCi 86 Dynamique 5dr [AC] Hatchback
	ETR	Mthly £191	Saving £2,214	Price £10,726
	Renault Clio 1.5 dCi 106 Dynamique S 3dr [AC] Hatchback
	ETR	Mthly	Saving £2,338	Price £11,337
	Renault Clio 1.5 dCi 86 Dynamique 3dr [AC] Hatchback
	ETR	Mthly £180	Saving £2,099	Price £10,241
	Renault Clio 1.5 dCi 106 Initiale 5dr Hatchback
	ETR	Mthly £249	Saving £2,433	Price £13,612
	Renault Clio 1.5 dCi 65 Campus 2007 3dr (Pre-model) Hatchback
	ETR	Mthly £158	Saving £1,963	Price £7,757

typical 11.64% APR

PCP finance quote over 48 months,  10,000 miles pa,  deposit of £1000