The lightweight home is roughly the size of a coffee table and has been designed to be flat-pack to make it easy to assemble.

Mr Matcham, otters and rivers project manager, added: "The flatpack design slots together easily and could be rolled out in urban spaces where the shelter that otters seek is in short supply.

"Traditionally these artificial homes are made from logs which rot easily or concrete slabs which are heavy to lift and do not provide the otters with much warmth."

He says the holt contains tunnels to help the animals feel more secure.

"It is also large enough to house any otter cubs that might come along," he said.

The design was paid for by Thames Water.

Nick Clark, the company's conservation officer, said: "We know numbers of this elusive animal have increased as the water quality in our rivers and streams have improved and yet the man made otter homes in place at 30 of our sites stand empty."