From the Wiki:
From flop to cult
C5 enthusiasts gather at the Brooklands Museum.
A heavily modified C5 fitted with a jet engine.
Despite its lack of commercial success when it was first released, the C5 gained an unexpected degree of cult status in the later years.[61] Collectors began purchasing them as investment items,[86] reselling them for considerably more than their original retail price. One such investor, Adam Harper, bought 600 C5s from a film company as a speculative investment in 1987. He sold all but four within two years, selling them to customers who wanted a novel or more environmentally friendly form of transportation. He also found willing customers among drivers who had been banned from the road, as the C5 did not need a driving licence or vehicle tax.[63] According to Harper, C5s could be resold for as much as £2,500 – more than six times the original retail price.[87] By 1996, a Special Edition C5 in its original box was reported to be worth more than £5,000 to collectors.[88]
C5 owners began modifying their vehicles to achieve levels of performance far beyond anything envisaged by Sinclair. Adam Harper used one C5 as a stunt vehicle, driving it through a 70 ft (21 m) tunnel of fire,[88] and adapted another to run at 150 miles per hour (240 km/h), aiming to break a world land speed record for a three-wheeled electric vehicle and the British record for any type of electric vehicle.[89][90] He said later: “Up to 100 mph it’s like you’re running on rails, it’s really stable. Then at about 110 to 120 mph it starts getting tricky. At that point if a tyre blew up or something happened you would be surely dead.”[90]
Chris Crosskey, an engineer from Abingdon, set a record for the longest journey completed on a C5 on a trip to Glastonbury – 103 miles (166 km) miles away (”I nearly died of exhaustion”[91]) – and tried three times to drive one from Land’s End to John o’ Groats, a distance of 874 miles (1,407 km).[61] Another engineer, Adrian Bennett, fitted a jet engine to his C5,[92] while plumber Colin Furze turned one into a 5 ft (1.5 m)-high “monster trike” with 2 feet (0.61 m) wheels and a petrol engine capable of propelling it at 40 miles per hour (64 km/h).[93]