though it builds vehicles elsewhere in Germany - at Bremen and at Emden in the north-west, close to the Dutch border - as well as having factories in Spain and Alabama, Mercedes is firmly based in Stuttgart. In fact, it can trace its activities there back for more than 100 years.

While it also manufactures MPVs, sports cars and coupes, not to mention its vast truck and bus interests and the A-class hatchback coming here soon, all the Mercedes saloon and estate ranges marketed in the UK are executive cars almost by simple definition.

Many people go for the entry level C180 saloon as their first step on the executive car ladder. The lower capacity models like this one are by no means flying machines, but the C-class offers some interesting engines, including the 2.3-litre supercharged Kompressor and a 2.5 turbo diesel.

One size up, the E-class is a notable car as a saloon, and particularly good as a roomy estate. Thanks to its excellent stability, it is one of the most restful cars for a long motorway drive in poor conditions, and one of the few cars in which you can arrive at the end of a journey feeling more relaxed than you were when you started out.

The bigger Mercedes engines produce plenty of power and torque without ever seeming strained. Their massive stamina helps the cars' remarkable residual values as well as fuelling the expectation that some of these engines, well maintained, ought to go three times "round the clock".

The AMG saloons, highly modified lthough still properly mannered road cars, are re-engineered by an outside firm but sold through the mainstream dealership network. They elevate Mercedes, especially the E-class, onto quite another plane of performance and handling.

Other cars in the Mercedes catalogue, of types which might not be considered executive material if built by lesser manufacturers, are fair enough entrants in the executive ranks. That probably applies to the only slightly retro-styled Mercedes on the market, the highly regarded SLK.

Its Fifties styling touches are lightly featured, the 2.3-litre Kompressor engine takes a suitably sporting approach, but the most fascinating thing about the SLK is the aspect that now you see it as a convertible, now you see it as a coupe. A highly ingenious mechanism pivots the steel coupe roof back into the boot - though once it is enclosed there you do have a problem about luggage space.

The CLK is a bigger-scale four-seater coupe. Its convertible counterpart is just arriving on the UK market. And the simply styled SL, especially in the form of the AMG-modified SL60, is one of the great road-going European sports cars.

Right at the top of the Mercedes range, the S-class, with a choice of wheelbase lengths in most variants, and going as high as six litres in engine capacity, outranks all the Continent's other luxury saloons.

However, Mercedes has been showing its Maybach concept limousine, reviving the name of its turn of the century chief engineer - in fact, the man who turned out the first car from the Daimler company to carry the Mercedes badge. This design study is for a lavishly equipped executive car of the 21st century.

The inch-and-a-quarter thick book produced in March this year to outline some of the new ideas put forward at the Daimler-Benz Innovation Symposium makes it clear that advances in design will not stop there.

Although the first few Porsche two-seaters were built in Austria, the famous sports car company relocated to Stuttgart in the early days of the original 356. It was an appropriate move for a firm which is one of the pure-breds of the world motor industry, because the city takes its name from a 10th-century "stutgarten" or thoroughbred horse stud.

Porsche builds an open sports car in the form of the Boxster, but it is the classic 911 Carrera with which successful business types are more likely to reward themselves. After all these years, its name still commemorates Porsche's class-winning performances in the great Mexican open-road race of the fifties, the Carrera Panamericana, which was itself called after the Panamerican Highway.

Despite all the company's efforts to move away from the rear-engined layout, faithful customers insist on regular design upgrades rather than anything radically different in approach. They still want the engine behind the passenger cabin, and body styling clearly related to the original 911 as launched on the market in 1964.

The result is that the present 911 Carrera is a very carefully engineered umpteenth-generation car. Although the old air-cooled engine has gone, unable to cope with modern noise and emissions requirements, that is no great problem. The latest water-cooled 3.6-litre flat-six is one of Europe's most notable power plants.

Like Ferrari and Jaguar, Porsche has a great sporting heritage, and enthusiasts for the marque still follow the fortunes of factory and private-team cars. In some years the company seems happy to sell cars for other entrants to race in major events, but this season it is heavily involved on its own account, with a strong entry for the sports car classic at Le Mans.