Turning the tides: Could hidden sea power energise our coastal towns?

In a secret location in the Highlands of Scotland, there's a fast-flowing river that's the key to understanding the massive power of water.

With a length of cord tied tightly across the river, he swam out, gripped firmly, and let the unstoppable current rush over as he sunk his head below the surface.

"As an engineer we do the maths and stuff," he says, "but sometimes you can get a lot more from actually touching the water and feeling it".

As he lay down in the powerful rapids, he visualised a new type of small-scale tidal energy generator.

It's an innovation he says could change lives for people in coastal communities.

"Trying to envisage how this turbine needed to interact with that environment - to understand the way the water was working."

Mummery's idea became the Swimmer Turbine - a 50kw tidal generator named after his experience in the river.

Anchored to the sea floor, the fiberglass and steel device lies invisible below the water's surface. It can generate enough electricity to power about 30 homes.

He began tests in the river in early 2010s. On a patent lawyer's advice he found a secret location, far from curious Highland tourists and their cameras.

"You're trying to be quite discreet because you're working with new technology," he says.

It was in the first years of his company, Flex Marine Power, long before Britain was gripped by the soaring costs of an energy crisis.

The size of the Swimmer Turbine is what sets it apart from large tidal projects dotted around Scottish waters.