Minsterley inventor Ivan, 71, is the ace of spades

So the weaponry expert turned his attention to the root cause of his problem – his spade.

The 71-year-old decided that, after being in use for millennia, this most basic tool was ripe for reinvention.

"I couldn't believe that in all the thousands of years the spade has been around, no-one had come up with a better design," said Ivan, who builds ancient weaponry and siege engines for historical TV documentaries. Once back on his feet, the former judge of the TV show

Scrapheap Challenge, spent weeks in his workshop building and testing prototypes.

In contrast to the back bending and twisting involved in using a conventional spade, Ivan's invention lets him dig while standing.

His design has two sets of handles and an L-shaped shaft that allows him to use his upper thigh and hip as a pivot point to lever the soil out of the ground without straining his back.

Ivan, of Minsterley, near Shrewsbury, has prudently filed a patent on his invention and is now hoping it could help gardeners everywhere by being developed for the commercial market.

"If you are like me, then after an hour's digging with a conventional spade you really feel the strain on your back," he said.

"I know my design looks a little bit unusual but it makes gardening so much easier, especially for older people who could remain active in the garden for many more years. I can dig like this all day with very little strain now that I don't have to do all of that bending and twisting.

"It's just as fast at digging as a conventional spade, if not faster."

The spade can be stored in two pieces and the blade attachment might easily be replaced with a fork or a weed puller. Ivan is now looking for a manufacturer to take his design to the next level.

Ivan badly hurt his back while digging his vegetable patch with a conventional spade last spring.

"I'd dug about two rows, I went to turn and then my back went. It locked up and went into spasm. I was in agony," he said.

"I'd trapped my sciatic nerve and had to spend three weeks incapacitated, on strong painkillers. I was so furious it got me thinking about the spade and how it could be redesigned to stop this sort of thing happening. My back still hasn't fully recovered – 10 months later!"

Dr Les Duckers, postgraduate research director at Coventry University believes the spade could be "an important step forward to safer and less tiring digging".

"Ivan's spade gives a clear advantage in terms of posture."

Ivan, an armour and weapons expert for the documentary series Battlefield Detectives, taught art and design before getting into TV and film work.

He appeared in early shows of Scrapheap Challenge – judging contraptions made from air compressors and old bicycles – and has worked on documentaries such as Leonardo's Dream Machines, Rescue Emergency and The Iranian Embassy Siege.

He also designed weapons and armour for the movie Aliens 3.

A fully working Roman siege engine that Ivan built for the Battlefield Detectives programme the 'Siege of Alesia' is one of the major exhibits at the new Shrewsbury Museum and Art Gallery.

His prototype spade is built from a carbon steel blade, a tubular steel shaft and a synthetic moulded section shaped to fit comfortably against the thigh.

His previous small-scale inventions include a survival knife that he designed with the survival specialist Lofty Wiseman and a simple-to-use etching press for schools and colleges.