WHEN the world's top selling two seat sports car is part of your line-up launching a replacement has to be faultless.

That's the challenge facing Mazda with the new MX-5, a roadster with a quarter of a century of fun in its pedigree.

The fourth generation MX-5 is coming on stream in a matter of weeks and it is true to form in every way.

Not only does it look fantastic it is also a delight to drive.

It is everything a true roadster should be - lightweight, nimble, rear wheel drive and most importantly, affordable.

Prices for the newcomer start from £18,495 which is just a fiver more than the previous model and only £3,570 more than the original cost when it was launched in 1990.

Allow for inflation and the £14,425 you'd pay for the Mark 1 MX-5 would be the equivalent of more than £30,000 today - and in the topless two-seater market that is the same bracket as the current Audi TT, Mercedes SLK and the BMW Z4.

Even the top specification new MX-5 with all the extras available costs less than £25,000 and comes with sat nav, sports suspension, heated seats and a high-end sound system from Bose that includes speakers fitted in the seat head rests.

As such the new Mazda is compelling stuff and classic roadster material to the core - a car which you just want to drive for miles on end.

It is low slung, has a soft top which can be folded in seconds and a 130-litre boot that is deep enough to carry two flight cases and a rucksack.

There's no fancy features such as multi-mode drive controls, turbo chargers or power buttons, just good old fashioned engineering and a yen for the open road in a car that is one of the best lookers around.

The foldaway hardtop featured on the Mk 3 model has been dropped to save weight but even so the hood is sturdy and well insulated.

Mazda is making the new MX-5 available either with 1.5-litre or 2.0-litre petrol engines and both are tuned for performance using the company's SKYACTIV technology designed to optimise power with economy - and economical it is.

Astonishingly, both engines outshone Mazda's official fuel consumption figures during our test runs - and that must be a first.

The 1.5-litre engine develops 131ps and is delightfully pure. Work it hard through the six-speed box and it is akin to the experience of the original model, nicely balanced and smack on for British roads.

In a car that weighs in at a fraction over a tonne this version of the MX-5 delivers open top motoring of the highest order with 0 to 60 acceleration of 8.3 seconds and a top speed of 127mph.

The 2.0-litre has a little more muscle at 160ps and is a second quicker 0 to 60 with the top end rising to 133mph. It costs from £20,095 and comes with stiffer sports suspension, 17-inch alloys and a limited slip differential to add a little more flexibility.

The gearbox on both is set up for quick changes and has a nice, short throw with a close gate that feels great to use.

From the driving seat there is a wonderful view of the car's sweeping wings which rise from the bonnet and every aspect of the cockpit is snug.

The handbrake is now to the driver's side of the centre console and there are now bottle holders for both occupants.

For fans of open top motoring it is impossible not to feel good about the way the MX-5 handles and with its 50-50 weight distribution the balance is beautiful.

Both engines are nice and lively but the real eye opener is the fuel consumption which was beyond expectations.

The 1.5 is rated at 47.1mpg and the 2.0-litre 40.9 with emissions of 139 and 161g/km respectively yet on lively drives of more than 100 miles across the Scottish highlands the trip computer showed an average 49.1 for the 1.5 engine and 41.9 for the 2.0-litre - and the average speed for both journeys was more than 40mph.

That is quite remarkable and with a ten gallon tank the MX-5 has excellent touring credentials.

While the cockpit is intimate and well laid out there's no glovebox. Instead there are concealed storage bins, one in the centre console and another in the bulkhead between the two seats.

With the roof up there is also a good amount of space aft of the seats but that's in the tonneau zone where the hood retracts.

All but the base SE models have a touchscreen sitting on the top of the middle of the dash and the top specification Sport Nav versions - priced from £22,445 and £23,295 - come with leather upholstery. A posh looking tan hide is an option for £200.

Body coloured door cappings are another feature of the mid and top grade cars and the interior is smartly finished with the MX-5 really looking the part in Mazda's now trademark Red Soul paint - a lustrous finish which costs an extra £600.

As two seaters go the new MX-5 is right out of the top drawer with its flowing angles, aerodynamic lines and all the bite that's needed.

Every version of the MX-5 has been bang on the money - which is why it is recognised by Guinness World Records for notching up more than 950,000 sales - and this one is a dream machine that's unbeatable at the price.