When you have reached the top of the tree there is only one way to go - unless, that is, you continue to outperform the opposition.

And that's exactly what's happened with the BMW 5-Series, which just seems to get better and better. Which is quite an achievement considering the car has been around for some 40 years and sold five million models.

The latest version offers everything from an eight-speed automatic gearbox to a fighter pilot-style head-up display in the windscreen showing your speed and the legal limit in the area you are in.

In the case of the 535d - the newest model to join the line-up - it also offers a brilliant combination of performance, economy and luxurious comfort to cocoon you from the outside world. It's almost as if you driving in a vacuum, aware of the cars around you while at the same time cut off from them.

The new car is some 58mm longer than the model it replaces and that difference means extra space for passengers, particularly those in the rear who can really stretch their legs.

The M Sport package means you get full body kit, a lower ride height and enhancements to the interior design. The body kit really sets the car apart from the rest of the range and even though there is a hefty premium to pay you do get a car to get you noticed.

BMW's M Sport range has always been particularly popular in the UK and there is little doubt that this new high performance diesel will be any different.

The 535d features the same engine as the 530d but with 299 bhp rather than 245bhp to make it a real diesel tour de force.

It not only hits 62mph in a rocket-like 5.7 seconds but does it in such a refined manner that you need to keep a constant eye on the speedometer - or the head up display - to make sure you don't collect a host of penalty points.

With drive dynamic control fitted the driver has a choice of running the car in Normal, Comfort, Sport or Sport+.

Switch to the Sport settings and everything firms up. The car holds on to each gear for longer and gives you an even more blistering performance.

But if you want real hands-on driving you can use the paddles behind the steering wheel and change gear manually. And while this is good in short bursts the automatic gearbox on this car, particularly in Sport, is so good that I rarely used the manual gearchange.

Once of the nice things about this rakish sports saloon is that while it looks - and is - every inch a high performance car it's also a sensible five-seater, with a boot which is enormous, and easily capable and taking everyone's luggage when it comes to holidays.

The 535d M Sport is one of those rare cars which has everything going for it. Its heated leather seats are supremely comfortable, it's spacious, refined and beautifully responsive.

And perfect 50-50 weight balance from this classic rear-wheel-drive car ensures that the handling is precise and more importantly predictable.