How much would you pay for a 1981 Porsche 924 GTR with just 109 km on the clock from new?

Well, when this ultra-rare model goes under the hammer in the United Kingdom at the end of July, Silverstone Auctions reckons it'll fetch somewhere between £475 000 and £575 000 (R10,3-million to R12,5-million).

The Carrera GTR was delivered new to Japan in 1981 by Porsche importer Garage Italya. In 1983, after being stored for two years, it was purchased by a Japanese businessman and classic car enthusiast who wanted to add it to his private collection.

The factory-built Porsche race car was enjoyed only a handful of times on the track at Suzuka and the Fuji Speedway. And it was on circuit that the car covered the 109 km (all in the first seven years of ownership).

So, what happened thereafter? Well, the 924 was carefully tucked away in the owner's two-storey garage. Removed from storage each year, the car was taken on a trailer to be serviced and then placed back carefully in position in the garage.

From 1981 to 2006 the car was serviced by Porsche specialist Tomei Car Service, and later by Porsche specialist Garage Tool Box. In the intervening period, the engine was started and run regularly.

Now in the UK and offered for public sale, the car comes with a Japanese title document and records of its minimal usage and extensive maintenance.

Just 17 examples of the 924 Carrera GTR were made available to private customers back in the 1980s. The cars were delivered from Porsche with fully integrated roll-cages, fully adjustable suspension and four-piston 935 brake callipers squeezing larger 31cm discs.

The engine was a highly modified version of the 2,0-litre motor used in all 924s, featuring dry sump lubrication. Weighing just 930 kg, the GTR could apparently hit 100km/h from standstill in 4,7 seconds.