At 10 o'clock on a Friday night in March last year Jennifer Groesbeck veered off a road in northern Utah as she drove back from dinner at her father's home and hurtled into the icy waters of the Spanish Fork river.

What caused her to swerve remains a mystery but, unluckily, the front wheel of her car caught the edge of the bridge's concrete wall, causing the vehicle to flip over it and crash down into the river. It landed upside down in the shallows with such force that the windscreen was blown out and the roof crushed as if it had been cardboard.

Out of sight from the road, the red Dodge hatchback sat in chest-high foaming water for 14 hours until it was spotted by an angler, who reported seeing a hand dangling out of a broken window.

Jennifer Groesbeck, above with her partner and 18-month-old daughter Lily, veered off a road in northern Utah and hurtled into the icy waters of the Spanish Fork river. Out of sight from the road, the red Dodge hatchback sat in chest-high foaming water for 14 hours until it was spotted by an angler

Four local police officers arrived first, their sense of urgency captured by the body camera one of them had switched on and whose footage has since been watched thousands of times on the internet.

They dash into the water - so cold that a total of seven policemen and firemen were later treated for hypothermia - and desperately try to get inside the crushed vehicle. Then, about two minutes into the body camera footage, its microphone picks up the faint sound of an adult voice, sounding urgent. It is unintelligible on the footage but appears to be a plea for help as Officer Jared Warner responds: 'We're helping, we're coming.'

Something very odd had just happened, although the emergency responders weren't to realise it at the time. With visibly new urgency, the rescuers turned the waterlogged car on to its side and discovered the 25-year-old driver was long dead.

Local police officers arrived first, their sense of urgency captured by the body camera one of them had switched on. Then, its microphone picks up the faint sound of an adult voice appearing to make a plea for help. Above, late mother Jennifer Groesbeck who lost her life in the crash, left with her daughter that survived, Lily

But there was a baby in the back seat, Mrs Groesbeck's 18-month-old daughter, Lily. Upside down and strapped into a child seat that had kept her out of the water and - crucially - kept her clothes dry, she had remained there for an age, her face suspended just above the churning river.

Unconscious and suffering from hypothermia, Lily was successfully revived at hospital.

Her miraculous survival made headlines around the world, and it wasn't until later that the four policemen discussed those frantic minutes and realised there was something very puzzling about them.

If the mother had died in the initial impact of the crash and the baby was unconscious, whose was the female voice they each swore they had heard coming from the car?

One of those policemen, Tyler Beddoes, believes he knows the answer: Lily was saved by a heavenly guardian who had comforted her during that bleak, freezing night in the half-submerged car and then called for help as her life hung in the balance.

The 25-year-old driver, above with her daughter and partner, was dead but there was a baby in the back seat, Mrs Groesbeck's 18-month-old daughter, upside down and in a child seat that had kept her out of the water

In a new book, Proof Of Angels, Beddoes - an officer with ten years' experience - describes how the rescue has solidified a religious faith he previously hadn't really felt.

One doesn't have to be a sceptical atheist to wonder whether someone might be trying to find a religious message here that isn't warranted. Beddoes is a Mormon, a religion that believes we all have a guardian angel.

The Lily Groesbeck case, nevertheless, defies any easy explanation. One impressionable or superstitious officer could decide to believe he heard a mysterious voice. But four witnesses are harder to dismiss, especially with video footage capturing a muffled voice and the officer's response to it.

Quizzed later, each of the rescuers concurred in what they had heard.

If the mother had died in the initial impact of the crash and the baby was unconscious, whose was the female voice they each swore they had heard coming from the car? Was Lily, above, saved by a heavenly guardian who had comforted her during that bleak, freezing night in the half-submerged car and then called for help?

Officer Bryan Dewitt said: 'We were down on the car and a distinct voice says: 'Help me, help me.' '

Jared Warner, the policeman who was in the video saying they were doing their best, said a few days later: 'All four of us can swear that we heard somebody inside the car saying 'Help'.'

'I think it pushed us to go harder a little longer. I don't think that any one of us had intended on flipping a car over that day.'

Beddoes soon became the spokesman for the four, as his colleagues grew wary of being labelled as naive - or mad.

But it appears that more people believe in angels than we might imagine. An online survey in the UK by the Bible Society and ICM reported that 31 per cent believed in angels and 5 per cent insisted they have seen or heard one.

In the U.S., a 2008 survey by Time magazine found 69 per cent of Americans believed in angels, with almost a third of them saying they had directly encountered one. Mystical experiences are widespread, but are a taboo subject even in a more religious country like the U.S., say academics.

Certainly, claims that some unexplainable presence - supernatural or otherwise - has come to people's aid at times of dire peril are so frequent that scientists have given the phenomenon a name: the Third Man Factor.

Inevitably, religious types have been more likely to explain this presence as angels, although even some non-believers have discovered a new spirituality after the event.

In a new book, Proof Of Angels, Beddoes - an officer with ten years' experience - describes how the rescue has solidified a religious faith he previously hadn't really felt. The Lily Groesbeck case defies any easy explanation

The experiences are reportedly so intense that not only do most know the gender of their 'angel' from their voice, but also feel their presence so strongly that some recall the pressure of their hand being held. The 'angel' is always benevolent and guiding, often giving specific instructions that the person insists he or she would never have considered. In many cases, including with Officer Beddoes, the experience is so profound it has been life-changing.

Those who claim to have experienced a Third Man include the victims of shipwrecks, bank heists, car crashes and shark attacks. Climbers, divers, even astronauts and polar explorers have told strikingly similar stories about encountering an invisible companion at a moment of intense physical hardship and mental stress.

Ron DiFrancesco, a financial trader at New York's World Trade Centre on 9/11, was on the South Tower's 84th floor when the second hijacked plane hit the 81st floor. As others were overcome by smoke as they tried to escape down a staircase, he lay down - only for something to grab his hand and lead him to safety through the flaming building.

Climbers, divers, even astronauts and polar explorers have told strikingly similar stories about encountering an invisible companion at a moment of intense physical hardship and mental stress

DiFrancesco recalled an 'insistent' male voice accompanied by a vivid sense of a physical presence which he called an 'angel'. He was the last person to leave the tower before it collapsed.

Stephanie Schwabe, a German scientist, was cave-diving in the Bahamas in 1997 when she mislaid her safety line - the only way she'd find her way back to the surface. With just 20 minutes of oxygen left, Ms Schwabe, whose husband had died in an undersea accident months earlier, sat on the cave floor and cried with rage and frustration.

Suddenly the cave grew light and she vividly felt the presence of another being. She was convinced it was her husband and she heard his voice urging her to calm down. She did so and, after scrutinising the cave, found her white line with just five minutes oxygen left in her tank and swam to safety.

In 1983, scientist James Sevigny was hurled 2,000ft down a Canadian Rockies mountain by an avalanche, breaking his knees and his back. He curled up in the snow to die, like his companion nearby, when he felt someone behind him and heard a female voice urging him to get up. It gave him a stream of practical advice that got him back to his campsite.

For two years, he couldn't talk about his experiences. 'It made me cry. It was so powerful. I just couldn't tell many people,' he said.

The aviator Charles Lindbergh reported sensing a presence in his cockpit during his famous solo transatlantic flight in 1927.

And in 1933, British explorer Frank Smythe narrowly missed becoming the first man to scale Everest when he pushed on alone as the rest of his party gave up. He recalls handing a piece of Kendal Mint Cake to his companion - only to realise there wasn't one.

The feeling he was with someone 'was so strong that it completely eliminated all loneliness I might otherwise have felt', he recalled.

John Geiger, a Canadian writer who has documented hundreds of 'Third Man' cases, says people have usually been very specific about their 'companion'.

More people believe in angels than we might think. A survey in the UK by the Bible Society reported that 31 per cent believed in angels. Pictured above: Jennifer Groesbeck with her partner and 18-month-old daughter Lily

And it hasn't always been solitary people. Antarctic explorer Ernest Shackleton wrote of experiencing a benign 'divine presence' walking unseen with him as he and two companions struggled over mountains in South Georgia in 1916. 'What was remarkable is that all three men independently said they had a very powerful sensation that there was another with them,' says Geiger.

Similarly, Harry Stoker, a celebrated World War I Royal Navy submarine commander, described sensing an invisible fourth man after he and two others escaped from a Turkish PoW camp. Curiously, so did both of the others.

Very occasionally, large numbers of people have claimed to see angels. Proof Of Angels recounts the bizarre case of the 1986 Cokeville elementary school hostage crisis in Wyoming, where a deranged ex-policeman and his wife took 136 children and 18 adults hostage.

When their homemade bomb accidentally detonated, miraculously only the two intruders were killed. The children claimed to have been helped by white-clad angels. The angels, they said, had told them to go near the window just before the bomb went off - an act that ensured they escaped with only minor injuries.

Little children in a Bible-bashing community may not be the most reliable witnesses. But what has made the Third Man syndrome so credible, says Geiger, is that so many of those affected haven't been superstitious types but level-headed adventurers and military types.

Sometimes, people believe they have sensed not their own guardian angel but someone else's.

Whether it's a case of guardian angels or simply finding a side of our consciousness we never knew existed, perhaps we're not as alone as we think

In 2008, 14-year-old Chelsea Banton lay dying of pneumonia in a North Carolina hospital room. Told there was no hope for her daughter, Colleen Banton had just instructed doctors to turn off her life support when she glanced at the room's security monitor and saw what she insists was an angel, complete with wings.

Mrs Banton kept the machine switched on and Chelsea's condition started to improve within an hour - a recovery doctors were unable to explain.

Scientists have yet to properly explain the Third Man phenomenon rationally. There are many theories, including extreme sleep deprivation. The concept is that the brain is divided into two halves, one which 'speaks' and the other which listens - this serves as a sort of neurological coping mechanism that kicks in when someone is suffering extreme physical and mental privation.

But none of these explain why people feel such an overwhelming benevolence from their companion, say sceptics.

Geiger notes that two of the factors - extreme cold and intense stress - common in many Third Man cases were present with the Utah policemen rescuing baby Lily.

As to why they all agree on what they heard, he says it's possibly an instance of subconscious suggestion, in which one of them inadvertently puts the idea in the mind of the others.

That's easy to imagine in some situations, but this particular rescue is surely different. There's that sound of a voice on the video footage, not to mention the obvious fact that at least one of the officers reacted to it immediately. There was no question of his imagining he heard it later.

One day, science may provide an answer for why so many people suddenly feel they have a powerful and life-saving friend when they are most in need of one. Then again, the phenomenon may never be explained.

Whether it's a case of guardian angels or simply finding a side of our consciousness we never knew existed, perhaps we're not as alone as we think.