Unique 1928 Mercedes S-Type headlines Bonhams|Cars Festival of Speed Sale

The S-Type comes from the company's heyday, when Mercedes had recently merged with Daimler and still had one Ferdinand Porsche as its chief engineer. He built the S-Type to be as at home on race tracks and hill climbs as it was driving on the roads to the events.

The heart of this classic's appeal is its Roots supercharger, which, for a few invigorating seconds, boosts power from 120PS (88kW) to 180PS (132kW) with the accelerator flat to the floor. It's plumbed to a 6.8-litre, six-cylinder engine sitting low in the chassis, leaving an inch of clearance between the motor and the horseshoe bonnet. 

The S-Type debuted at the Nürburgring in 1927, taking a class win in the hands of Rudolf Caracciola. Despite this success, the Great Depression which followed hindered sales, and just 174 cars were ever built.

The car crossing the blocks is order number 4,1569, chassis number 35,985, and engine number 72,191. Delivered to Mercedes UK, its first owner, Mr Harcourt-Smith of London and Cairo, is presumed to be Sir Cecil Harcourt-Smith who was the British envoy to Cairo in 1926. 

Its second owner was the 9th Duke of Grafton, who, at 20 years old, campaigned the car at the Inter Varsity trails with pictures in that year's Motorsport Magazine documenting its appearance. 

These pictures confirm the Mercedes doesn't have a regular factory body. They show a long touring body with wings extending beyond the body line fitted with unique side lights and a SSK-like shrouded tail. The single enamel star on the radiator was only fitted to late S-Types and its successors, the SS and SSK. This example is believed to be the only car of its type in existence. 

The car would be sold after the sad demise of the Duke of Grafton behind the wheel of his Bugatti at the age of 22, while competing in the Limerick Grand Prix. It was advertised for sale in The Autocar in 1936, the advert stating: "whole chassis recently overhauled and guaranteed 100mph". 

The car passed through the hands of two illustrious owners before it was purchased by pioneering collector C. W. Peter Hampton, who, after sustaining a shrapnel injury to his left arm in the D-Day landings, had the car's central gearchange extended to the right-hand side. The notched door was also removed, although it remains with the car. Hampton died in 1991 when the car's ownership passed to Tom Scott Senior. 

Now, presented showing the correct numbers and having been recommissioned by the skilled technicians at Jim Stokes, the car represents a superb opportunity to experience one of the legendary Kompressor cars. It could easily be returned to its fabulous original guise by its lucky future owner.