When Charlie Howarth took the call about an “old” BMW a woman was looking to sell, he didn’t think much of it.

But when the Coys of Kensington classic car auction house specialist arrived at the East London address, things changed very quickly. Sitting there was a legendary BMW land speed record car that that had fallen off the collector car world's radar a quarter-century ago.

The special 1979 M1 was created at the behest of Austrian racing driver Harald Ertl, who teamed up with British Petroleum to modify the mid-engine coupe to run on liquefied petroleum gas, or autogas, which the company was looking to promote as a motor vehicle fuel.

(Coys of Kensington)

BMW only produced 453 M1s from 1978 to 1981, with the help of Lamborghini, and stock versions are prized collectibles that can sell for $700,000 or more. By adding twin-turbos to the M1’s inline-6-cylinder engine, Ertl’s team were able to increase its power from 277 hp to around 410 hp, which was a lot in 1981. The bodywork was also customized to improve its aerodynamics, and associate sponsor Blaupunkt installed a batch of its speakers for good measure.

BMW built just 453 M1s. (BMW)

On October 17, 1981, Ertl took the violet car to Volkswagen’s Ehra-Lessien high-speed test track, which is a 12-mile-long circuit that features a perfectly flat 5.6-mile straight, and set a mark of 187.3 mph. However, there wasn’t a sanctioning body present to verify the record, so it was never officially recognized.

STASH OF CLASSIC CAR PARTS WORTH MILLIONS FOUND IN SHIPPING CONTAINERS

Tragically, Ertl was killed in a plane crash the following year before he could try again and the car sold.

After changing hands several times and ending up at a dealership in England, it was purchased by a pharmacist in England named Pummy Bhatia in 1993, who passed away just 2 years later.

(Coys of Kensington)

It spent most of the next decade parked outside before it was put in a garage next to a DeLorean he also owned about 14 years ago. Howarth said Bhatia’s son hoped to fix the BMW up one day, but the prospect just kept getting more expensive with each passing year.

(Coys of Kensington)

So he and his mother finally decided to sell it and will be auctioning it at Coys'Techno Classica event in Essen, Germany, on April 13, where it will surely be the most unique lot up for grabs at the prestigious collector car event. Howarth said it's far from running condition and needs a lot of work, but that the brakes work and it rolls freely, making it a prime candidate for a serious restoration.

APP LETS YOU INVEST IN COLLECTOR CARS: