A shelter inspired by celebrity adventurer Bear Grylls saved the lives of a father and son when they became lost in the Tasmanian wilderness, police have said.

John Ward and his 13-year-old son Stephen survived three days under harsh conditions on the isolated island off the south coast of Australia after becoming disorientated during a hike.

Constable Michael Preshaw, of the search and rescue team that found the pair, said he was “amazed they made it that far” and believed the shelter was key to their survival in near-freezing temperatures.

“They'd actually made quite a good shelter down in the creek bed,” he told ABC.

“They were dry when we found them, so they'd done a good job.”

The police officer described the shelter as being “straight out of the Bear Grylls handbook”, adding that it was made entirely of sticks and ferns.

Joanne Ward-Pearce, John's wife and Stephen's mother, confirmed the pair had watched a lot of the Eton-educated British survivalist's TV shows.

Mr Grylls is popular in Australia where his programme Born Survivor was broadcast as Man vs. Wild for seven seasons.

Mr Ward and his son were finally found on Thursday about 15 kilometres from the site they set out from on Monday.

Constable Preshaw said his team had believed the chances of finding them alive to be slim.

“When I saw their shelter, I still wasn't convinced they were going to be OK at that stage,” he said.

Mr Ward was found sprawled across the track, Constable Preshaw said.

The 41-year-old was taken to hospital with mild hypothermia and has remained there for monitoring.

Stephen, however, was well and described as in good spirits.

He said he and his father had huddled together for warmth and eaten a few muesli bars they had with them, but he had begun to fear for their lives.

“I thought we were on the way out,” he said.

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Although the pair were inexperienced and under-equipped to sleep outdoors, Constable Preshaw said he was impressed by their shelter.

“The shelter was tiny, it had two sticks which joined onto another two sticks that went back into the bank, then they'd criss-crossed other sticks and wood over the top of it and put ferns and leaves and other things on top to make it water-proof,” he explained.

He said the improvised dwelling was something he and his team would build if they found themselves in a similar situation, adding that the small size helped keep the pair warm and dry.

“It was only big enough to crawl into — about two metres wide and about a metre-and-a-half long. It's probably what kept them alive,” he said.

Ms Ward-Pearce said the three days her husband and son were missing were “the longest time” of her life.