ONE OF THE finest supercars of the modern era is the McLaren F1, in its ultimate expression, the LM-spec, featuring a high-downforce wing package and more power from its BMW V12 engine. Only six were produced.

Three years ago, this superb example, one of two upgraded by McLaren Special Operations, sold for a whopping $13.8 million.

Now it’s up for grabs again, for an undisclosed amount and like last time, Sotheby’s Private Sales is hunting a deep-pocketed buyer.

After starting life as the 63rd and penultimate McLaren F1 built, Chassis 073 was completed in 1998, then sent to McLaren Special Operations for upgrading and personalisation.

The buyer of Chassis 073 ordered a Big Mac with the lot – including an LM-specification engine further boosted with parts from the GTR LeMans race cars to provide 680hp at 7,800 rpm.

McLaren added the Extra High Downforce package including revised nose, more aggressive rear wing, plus a four-millimetre Gurney flap for high-speed stability. Its brilliant orange metallic perfectly captures the contours of the F1.

The interior was upgraded to GT specifications and re-trimmed in magnolia leather and Alcantara, with beige Alcantara inserts in the seats. Other improvements include upgrading the air-conditioning and stereo and the inclusion of satellite navigation, plus a helicopter-grade car-to- car radio and intercom system.

McLaren also fitted the car with a larger 14-inch steering wheel, an LM-style handbrake instrument cluster with a shift light and tinted side windows. They also etched '073' into the tachometer.

The final touch was by Gordon Murray: he signed the car on the console just ahead of the ignition switch.Since the upgrade it has travelled 700 kilometres, in addition to the 6000km it had before the transformation.

This upgrade has created a unique car offering the ultimate in luxury and ferocious performance and it is being sold ready to drive.

It comes with its original exhaust, gold-plated titanium Facom tool roll, a Facom mechanic’s rollaround tool chest with a torque wrench, luggage, and its original owner’s and service manuals.

Conceived by McLaren owner Ron Dennis and Chief Designer Gordon Murray from a blank canvas, the F1 was expressly built to be the world’s fastest road-going production car and on 31 March 1998 it set a world record speed of 240.14 mph at the Ehra-Lessien Proving Ground in Germany. It still holds the record as the fastest naturally aspirated production car.

Last year at the Pebble Beach Concours, Bonhams auctioned the first McLaren F1 imported into the US for a staggering $15.62 million, a record. Could this be the record breaker? Only time will tell.