Sinclair Research's products have always been noted as being breakthroughs, not in an entirely scientific way, but more ones that downscaled technology such as calculators and computers to make them fit into the home environment. However, being an entrepreneur, Sir Clive Sinclair, the company's owner and head visionary, had several projects of his own at the back of his mind.
	At the start of the 1970s, there was a drastic need to try and resolve environmental issues that were becoming apparent at the time. The major political parties knew this, and also knew that there were votes to be gained by seeming to be more environmentally friendly. Soon grants became available to companies that could be seen to be pursuing 'environmentally sound' goals. One of the key fields to gain from this was research into the replacement of conventional petrol engines by electric powered cars.
	By 1980, Sinclair Research was becoming more and more popular due to the success of their pocket calculators, and the newly released ZX80 home computer. One of Sir Clive's dreams was to be the leading force in electric powered car design, and he saw his company's increased reputation as a stepping-stone to further this dream. Unfortunately, the company was at the time just coming to grips with the weight of supply and demand incurred by the ZX80, and resources were scarce to try and tackle such a radical proposition. Still, Tony Rogers, formerly a designer for Radionics, was brought in on a consultancy basis. The page of research was slow, as Rogers held a permanent job running the Exeter Academy, and no doubt viewed the research as a distracting hobby more than anything substantial.
However, in March 1980 the government abolished motor tax for all types of electric transport, and the Sinclair dream looked like it could become more of a viable proposition. Research was stepped up over the next eighteen months, but soon hit a stumbling block that had impeded the area of electric transport before. The existing battery-powered technology was far behind the times compared to petrol transport, petrol having much greater energy density. A kilogram of petrol offers the potential of 13,000 watt-hours, whereas the lead-acid equivalent holds on 50 watt-hours. It was at this point that Sinclair made his first mistake in the project: he opted to make do with existing battery technology. His view was that a successful electric vehicle would push battery manufacturers to produce better batteries, and that for his company to do the same would be a waste of money. This decision effectively negated any real technological innovation in the design of the vehicle.
	By the beginning of 1983, the time had come that serious investment would have to be made in order for the product to ever see the light of day. However, support from the rest of the company was almost entirely absent. The ZX81, the follow-up to the popular ZX80, had established Sinclair's name on the high-street, and the company's success in this area looked to continue for the foreseeable future. The company didn't want to upset its stability with a project most regarded as a 'challenging diversion'. Sinclair decided to sell a small percentage of his holdings in the company, which, at a time when Sinclair's shares were at their peak, provided him with the money needed to set up an off-shoot company, Sinclair Vehicles, to continue the project. 
Then came another incentive provided by the government: the company learned that 'electrically assisted pedal cycles' would be singled out for special treatment under new laws. Owners of such machines would be exempt from insurance, road tax, crash helmet, or even a driving license. So the company altered its design to suit, thus designing the vehicle for convenience to them rather than for any customer consideration. Most of the design of the battery and electric motor were completed by outside firms, and Sinclair used these firms' reputations to hype up the product. However, the said products weren't at the top of the firms' ranges, and the battery was essentially a standard car battery, while the motor was a modified washing machine motor! The company was helped out by the Welsh Development Agency to secure a deal with Hoover for manufacturing the vehicle, seduced by Sinclair's production projections of 200,000 - 300,000 units per year.
So, the Sinclair C5 was born. It cost £399, and was initially only available on mail-order. Measuring 5'9 by 2'5 by 2'7, the main pre-launch criticism was that the vehicle wouldn't stand up to anything resembling heavy traffic. The British Safety Council issued a very negative report, which was sent out to its 32,000 members two days defore the official launch. The launch itself was glossy and expensive, costing the company £3 million according to official records. Sir Clive decided to astound the public by releasing the open-topped trike in the middle of winter, and so the launch took place on 10 January 1985. Any preconceptions journalists may have had of the vehicle were confirmed when it turned out that many of the demonstration models at the launch didn't work! 
Soon after the launch, criticism started coming from all corners. The press had a field day, many journalists who had test driven the vehicle complaining about its performance and reliability, and many more voicing concern about its safety on the road. The main source of criticism however came from consumer and motoring agencies. The AA's report questioned every technical statistic of the C5, for example reasoning that the vehicle's battery range was half what the manufacturers claimed it to be. The report stated that there was 'no comparison' with other mopeds on the market. The Which? Report was even more scathing, declaring the C5 'of limited use in its present form; poor value for money'. The public were similarly displeasing with the vehicle's performance, and after two months Sinclair had only shifted 5,000 units, in comparison to the projected 200,000 per year.
By March 1985 it was clear that the project was not going at all to plan. There had been a number of complaints regarding performance due to the plastic moulding attached to the gearbox, and production had to be halted to fix the problem. By April, demand for the C5 had ground to a virtual standstill, and soon enough Sinclair Vehicles was liquidated. Under a year after the C5's launch, the manufacturers had gone bankrupt.
It is not difficult to see why the vehicle failed. It was designed purely to exploit a loophole in EEC regulations, and not thought of the target consumers was given at any stage in the development. It was not what the public wanted or needed at the time despite its eco-friendliness, and serves as a reminder that one man's dream does not necessarily make a good reality. 

http://www.nvg.ntnu.no/sinclair/vehicles/c5_sst.htm
http://www.sinclairc5.com/
http://www.sincuser.f9.co.uk/036/sincc5.htm