The Black Shadow was capable of 125mph, and easily recognised by its black engine and gearbox unit, and large 150mph speedometer, but in 1949 a White Shadow – a machine to Black Shadow mechanical specification, with the Rapide colour scheme – was available. However, only 15 were ever sold, and the option was dropped in 1952, making this an extremely valuable machine.

“At our last auction in March we sold an Ariel for £13,500 and this was our highest price for a motorbike to date,” said auctioneer Richard Edmonds. “But I am expecting the Shadow to top that as it really is a terrific bike.”

It is included in the auction that will be held at Castle Combe racetrack on June 29-30 for an estimate of £60,000-£70,000. 

Other motorcycles have been consigned to include Triumphs, Matchless and a Scott.

A fully illustrated catalogue is available online. Entrance to the auction is by catalogue only, available on the door for £10 (admits two).