Then in 1985 a small three-wheeled electric car made a large dent in his reputation and bank account. In many ways, Sir Clive's C5 was the future. It was stylish, cheap, eco-friendly and an answer to urban congestion. But he did not test his market. People scoffed and the press drove the little car off the road.
They said it was an open-top bicycle in disguise, and that it was slow and too low to be safe. Urban congestion was all very well, but what about the nasal variety? Who wanted their nose stuck in a juggernaut's exhaust? The press said the C5 had been sold without wet-weather gear. Not true, but people believed it anyway. Another PR mistake involved its "hi-vis" masts. Like the flagpoles on kids' shopping trollies, the masts were to make the car visible. But they were only an optional extra and by the time Sinclair included them as essentials, sales had taken a further knock.
Another fallacy haunted the car. People sneered because it was powered by a washing-machine motor. It wasn't. It was driven by a motor made by a company that made washing machines. They also made torpedo motors. Shame the C5 didn't get that reputation.
There were other problems. On a cold day the C5 might struggle to travel seven miles. If the battery did conk out, the car - which came with pedals - was heavy to cycle.
In the end, only about 15,000 C5s were produced and the project cost the company pound;7 million. Sir Clive was eventually forced to sell up to rival Alan Sugar's Amstrad. The C5 is now a collectors' item. Toot, toot.