An engineer shortlisted for a global prize by the Prince of Wales said his invention was created at his mother-in-law’s dining table.

Adam Root built filters that remove microplastics from water pumped out by washing machines and industrial units, preventing them from reaching the ocean.

“It’s one of the greatest challenges of our generation and people don’t really understand or know about it,” said the 35-year-old, from Saffron Walden in Essex.

His company, Matter, could win £1m at the Earthshot awards on 5 November, whose winners are commended for innovative solutions they create to help the planet.

Microplastics have been found on every part of Earth, including buried in Antarctic sea ice and inside the guts of animals living in the deepest ocean trenches.

Concerns have persisted over their potential risk to human health, being prominent in bottled drinking water and marine life.

Mr Root told BBC Essex’s Sonia Watson that microplastics had become one of the “biggest pollution sources on the planet”.

“I was looking at how we solve that and started developing solutions,” said the inventor, who built the prototype after leaving his engineering job eight years ago.

He said creating Regen – his self-cleaning, reusable product – was “challenging” and was the result of four years of work in a laboratory.

“I was also working off my mother-in-law’s dining table for about nine months,” recalled Mr Root, whose head office is now in Bristol.

“I then upgraded to working out of a stable for a little while in the rural parts of Essex, and eventually made it ‘big time’ and got a unit on a turkey farm.”

Mr Root was supported by a £250 grant from The Prince’s Trust, now The King’s Trust, to begin building his invention.

He also had the support of his wife, who gave up her job and helped.

The business started off building filters for household washing machines, but has since raised more than £15m for its work and employs about 45 people.

“We have also scaled [the filter] up to work on an industrial scale, so that’s millions of litres of water, rather than hundreds of litres of water,” Mr Root added.

He said the device was now being used in textile factories across the world.

“Me and my wife have been together since we were 14, so we’ve been through some wild stuff,” the inventor said.

His company is one of three competitors shortlisted in Earthshot’s “revive our oceans” category, each of which were selected by Prince William.

Some of the finalists in other categories include entire countries and cities.

“It was a little bit strange. There’s the country of Barbados, a city in China… and here’s Adam,” Mr Root said.