IT could be a case of lucky numbers for BMW as it shuffles its pack to make room for the convertible version of the 3-Series, which is now branded a 4-Series.

By following Audi's form of designations (odd numbers for traditional shapes and evens for the more exotic), the marque has elbowed space to slot in the little 2-Series, which is effectively the coupe and convertible version of the lead-in 1-Series. Anyway, enough of this marketing-speak...and a bit more about the car itself.

I drove the 435i M Sport, which is the raciest version available until the M4 convertible hits the road shortly. Powered by the renowned 3.0-litre twin turbo straight six - an engine that has scooped awards - it belts out a useful 302bhp, so performance is pretty rapid. Sixty-two springs up in under six seconds and max is an electronically restricted 155mph, so it's a sprightly set of wheels.

The nature of the 435i, though, is more refined than raw, leaving ample scope for the M4 to scare your pants off. A slick and super-smooth double clutch automatic gearbox complete with paddles on the steering wheel completes the equation to make this four-seater Beemer just about the perfect boulevard cruiser or motorway express.

A tad wider and longer than the outgoing 3-Series convertible, the designers have made good use of the extra centimetres allowing greater rear space, particularly legroom and an enlarged boot which can now absorb 370 litres of cargo.

This area is vastly reduced when the tin-top is folded and you are then left with a pillar box slot through which to ‘post' your luggage.

The secret is to travel to you weekend destination with the roof up, unload, then enjoy open air motoring. When folded, there's little wind intrusion and the top can be lowered or raised while driving slowly.

Getting in and out of the rear seats can be a delicate operation but the seats are comfortable and supportive. The front of the cabin is pure 3-Series saloon which is high quality and appealing but lacks excitement or innovation.

There is a penalty for the convertible - apart from the price of £45,470 - and that is the extra 200kg or so weight.

With more than 300bhp, it would be unfair to say the extra kilos blunt performance, but it feels a shade less responsive and muscular than the Coupe version.

The handling is hugely confident and balanced and the rear-drive format works with usual BMW brilliance. Few drivers will get to reach the outer edges of 435i's cornering limits, such is its ability.

Engine noise is a rorty snarl under full throttle but the rest of the time it is quite muted - much more so than my own Z4 35i. Fuel consumption is an impressive 36.7 combined mpg which pans out at close to 30mpg during normal running. The CO2 emissions are 180g/km.

Such is the refinement and classy appearance the new 435i that in some ways it is closer in nature to its big brother the 6-Series which could mean it will appeal most to older buyers...lucky them.