Iain Sinclair with the innovative CardSharp folding pocket knife.

It’s cutting-edge technology – literally – that fits in your wallet.

Just three ingenious folding operations transform a piece of plastic no bigger than a credit card into an elegant pocket knife with a razor-sharp stainless steel blade.

The CardSharp is the brainchild of Hildersham designer Iain Sinclair – the younger brother of inventor Clive Sinclair, whose name is forever linked with his failed C5 electric vehicle.

But Iain, 68, is quick to point out that it was his brother who pioneered personal computers in the early 1980s – as well as coming up with the first slimline calculator and the first pocket TV.

Inventing obviously runs in the family. Iain was designing mouse cages at the age of nine, complete with wheels and tubes for the animals to slide down – things you couldn’t buy in those days.

“I was always aware of the aesthetics of consumer products and very early on I started making things,” he said.

“It was a bit of a family joke that I would always be on the next model – always redesigning and improving things – which is what I still do now. We go on and on trying to improve our products.

“And Clive was always interested in miniaturisation – obsessed with it. He’d go to the Ideal Home Show and come back with all these miniature packets of cornflakes and things. He loved miniatures – which went through into his work.”

Another early project for Iain was building soap box carts – he designed one with a footbrake rather than the traditional handbrake lever.

“I built in this footbrake which was a plank on a hinge that you rammed on to the ground,” he said. “It used to wear out very quickly – so it was a pretty lethal thing really.”

Iain eventually went on to do design work for Clive – it was Iain who designed the cabinet for his slimline calculator, which is now on display in the Museum of Modern Art in New York.

The calculator proved a great success, despite its £80 price tag in 1972 – the equivalent of £800 today. “You couldn’t get anything like it – it was the first really slim calculator,” said Iain.

Over the years Iain has worked on projects for clients all over the world and, just like at the age of nine, he’s still redesigning things – although not always for the better.

“Whenever you design, however simple it might be, there’s always something you haven’t thought of – it doesn’t matter who you are,” he said. “And if you change anything on a design, it can affect it in some way you haven’t allowed for.”

Iain discovered this the hard way when he adapted his range of flat-pack lamps for the Liberty store in London. The lamps were coated with Liberty material.

“I proudly went into the shop to see them and there they were all lit up,” he said. “But to my horror there was smoke coming out of them.

“These things had collapsed because of something to do with sticking the material on – it had caused the plastic to shrink on to the bulb. So we didn’t get any repeat orders on that one.”

These days Iain’s company – Iain Sinclair Design – is concentrating on building up a range of own-brand products.

As well as the folding knife, the range includes a credit-card-sized aluminium torch that packs a powerful beam, with the highest power-to-weight ratio of any flashlight or torch in the world.

It’s all a far cry from that plank on a hinge.