There is a room in Powderham Castle, Devon, that dogs refuse to enter. It’s not even a room, really, more a threshold between one section and another on the second floor. Whenever Lady Devon, who lives there with husband the Earl of Devon and family, crosses this threshold, Bobo and Daisy, the two dogs of the household, stop at its border, turn around and take an alternative route.

Several months ago, in a guided tour of the 14th-century castle, a visually impaired woman came to this border with her guide dog. It, too, stopped in its tracks and refused to let her go any further. Trained to protect its owner, it pulled her away from the room. Tour guides have reported babies, otherwise calm, beginning to cry. And tourists - unaware of the room’s reputation - have inexplicably refused to remain within its tiny confines.

None has explained why, apart from a cold feeling of dread that demanded they exit immediately.

The Courtenay family is open-minded about the existence of a ghost in this part of the family estate. Lord Devon says his grandfather was responsible for some of the stories about ghosts in the castle in an effort to entertain his grandchildren, “but that does not explain the unusual goings-on here”.

“There has always been a bit of a mystery about it and I think he merely embellished stories that had been around for ages,” he says. “After all, it would be unusual for a house lived in for over 600 years not to have a few ghosts about.” And there is one fact about this otherwise unremarkable room that perhaps gives this ghost story a bit more credence - in the mid-19th century, during renovations, the skeleton of an unidentified woman and child were discovered hidden under the floorboards... Everyone knows a good ghost story. We’ve all heard the one about someone picking up a hitchhiker on a lonely road, only to find they have disappeared on arrival and that a person matching the mystery hitchhiker’s description was killed years earlier on the same stretch of road. Or have you tried going into the bathroom, turning off the light, spinning around 14 times while saying “Bloody Mary” on every revolution? On the 13th turn, you’ll see an apparition appear in the mirror... A Gallop survey in 2001 showed that about 38 per cent of Americans believe in the existence of ghosts, while a Mori poll in 1998 found 13 per cent of Americans claiming they’ve had an up close and personal experience with one.

Closer to home, millions of readers of the Daily Mail questioned the existence of ghosts when a fuzzy picture of a man in a long coat appeared in its pages last December. The man, walking through a doorway in Hampton Court Palace, was caught on a security camera. It could not have been a guide, as they don’t enter that part of the palace. Staff investigating an alarm which indicated the fire doors had been opened found nothing untoward and, somewhat confused, checked the film footage. The cameras showed the great doors heaving open... but no one was there. Then the long-coated figure appeared, seemingly from nowhere, and slammed the doors shut. At the same time the next day, the doors flew open again, but no one appeared.

One of the most experienced ghost investigators in the country, psychologist Dr Richard Wiseman from the University of Hertfordshire, proclaimed that it could be “the best ghost sighting ever”. He and a team of scientists have prodded about in several of the UK’s allegedly haunted areas with a view to using cold, hard facts to disprove (or prove) the existence of ghosts. One of his team, Dr Caroline Watt, senior research fellow at the Koeseler Parapsychology Unit of the University of Edinburgh, says she’ll “never say never”.

“As a scientist, you should never say anything is impossible,” she says.

“The interesting question is how could one ever be certain that ghosts don’t exist or disprove it. I don’t think you could.” That said, Dr Watt isn’t quite sure what scientific data would make the hair on the back of her neck stand up. “I’m interested in occasions when people report seeing something very specific in a location - say it’s a one-legged man and he’s got a green parrot on his right shoulder - and then someone else who’s had no other contact with that person says the same thing. If you get independent witnesses and you’re able to rule out all other linkages, then I find it quite surprising that people could come up with identical reports.”

However, just when it sounds like Dr Watt may be talking herself into believing -even slightly - in ghosts, she returns to scepticism. “What you find out when you investigate more closely is that the witness actually told somebody else what they saw.” Still, in two of Dr Wiseman’s and Dr Watt’s investigations -Hampton Court Palace and Edinburgh’s forgotten city, the South Bridge Vaults -there were goings-on in a controlled scientific environment that could be interpreted in either way.

Hampton Court Palace yielded the most interesting results. It was chosen because it is believed to contain the ghost of Kathryn Howard, the fifth wife of Henry VIII; 15 months after their marriage in 1540, she was found guilty of adultery and sentenced to death. On hearing the news, she pleaded with the King for her life, but was dragged back along a section of the palace now known as “the Haunted Gallery”. By the turn of the 20th-century, the gallery had become associated with unusual experiences, including sightings of a “woman in white” and reports of blood-curdling screams.

Reports of hauntings have been well recorded at Hampton Court. Catalogues exist of all reported incidents from the end of the 19th century to the present, containing material from newspapers, magazines, books and interviews with witnesses.

So while the areas of the palace that are supposedly haunted are well known, the key to this investigation was to find participants who had no prior knowledge of where these areas were or what they might be looking for. This would be the strongest indication of other-worldly goings-on - if “seemingly trustworthy witnesses consistently report experiencing unusual phenomena in certain locations” without prodding or prior knowledge.

The experimenters explored the psychological mechanisms that underlie apparent evidence of “ghostly” activity - in plain English, they tried to find out why people believe in ghosts and if the factors influencing this belief were enough for science also to believe. The investigation required gathering members of the public, explaining to them they were involved in an experiment investigating ghosts, and getting them to fill in questionnaires about their experiences.

Participants didn’t let the scientists down. The results revealed significantly more reports of unusual experiences in areas with a reputation for being haunted. About 45 per cent reported something strange, and two-thirds of these involved an unusual change in temperature. Others mentioned various phenomena, including dizziness, headaches, sickness, shortness of breath, and some form of force, a foul odour, a sense of presence and intense emotional feelings.

When asked whether their experiences were due to a ghost, of the 215 participants, about 4 per cent indicated “Definitely yes”, 10 per cent “Probably yes”, 37 per cent “Uncertain”, 41 per cent “Probably no”, and 8 per cent “Definitely no”. Their experiences were marked on a floor plan of the castle and percentages were calculated. The probability of things going bump in the daytime was deemed to be “significantly greater than chance”.

So what can we conclude? The criteria stated at the opening of the experiment -that seemingly trustworthy witnesses consistently report experiencing unusual phenomena - appear to have been met. So ghosts do exist, according to science? Not quite. Terms such as “group contagion effects” and possible reasons such as sensory deprivation and magnetic field fluctuations sow seeds of doubt.

Magnetic field fluctuations, caused by a variety of factors, such as heating by the sun, tectonic plate movement, hairdryers, computers and televisions, are believed to “trick” the mind into experiencing ghostly goings-on - but this is controversial theory. Indeed, ghosts themselves could be a source of magnetic field fluctuation. “We don’t know much about whether ghosts might be producing such a source,” admits Dr Watt. “But what we do know is that once you’ve got that source it produces a scary feeling that people could quite easily interpret as being a ghost in the environment.”

Dr Michael Persinger, a Canadian researcher, has been one of the world’s leaders in the effect of magnetic fields on the human mind. He argued nearly 20 years ago that changes in geomagnetic fields could stimulate the brain’s temporal lobes and produce many of the subjective experiences associated with hauntings. In an interview in Psychology Today, Dr Persinger explained: “Individuals prone to paranormal experiences are sensitive to weak electromagnetic fields and to man-made electrical fields, which are becoming more prominent in the communication age.” He once concluded that a teenage girl who consistently sensed the outline of a baby over her left shoulder at night was, at least in part, being affected by the presence of a clock radio near her bed. While Dr Persinger has been able to prove in a controlled laboratory environment that electrical stimulation can produce ghostly feelings, imagine how those feelings can be interpreted in a dark room, in an old house, in the middle of the night... The conclusion? Science doesn’t believe in ghosts. “The data strongly supports the notion that people consistently report unusual experiences in ‘haunted’ areas because of environmental factors, which may differ across locations,” says the wrap-up to the Hampton Court Palace investigation.

“These findings strongly suggest that these alleged hauntings do not represent evidence for ‘ghostly’ activity, but are instead the result of people responding - perhaps unwittingly - to ‘normal’ factors in their surroundings.”

But in science - particularly the world of para-science - even this seemingly conclusive conclusion isn’t complete. Says Dr Watt, who co-wrote the report: “I don’t see how one could rule out the possibility that, for example, if there’s a geomagnetic anomaly it’s a ghost that’s causing that anomaly. As psychologists we could put on our sceptical hats and say “look, there’s environmental causes at play here”, but it would be almost impossible to rule out a real spiritual interpretation. People who believe in ghosts or think they’re psychic may actually be more sensitive to environmental variables.”

A clear conclusion is as elusive as proving or disproving the existence of ghosts. So, in her educated and scientific opinion, does Dr Watt believe in the existence of ghosts? “If you define a ghost as a being after death then I don’t believe in ghosts because I don’t believe in life after death.”

In X Files-speak, it’s time to find the Fox Mulder to this argument to counter the Dana Scully approach of Dr Watt. But who to call? The man who inspired the film Ghostbusters, Dr Larry Montz, is the most obvious first contact. He, too, uses science to investigate ghosts but instead of using data to dampen the spirits, he conscripts it to talk up the possibilities.

And he’s certainly in no doubt about which side of the paranormal fence he’s on:

“I’ve had investigators knocked down in front of me, he says. “And I’ve been pushed downstairs and hit with objects,” he says. “That’s only very seldom, though.”

Dr Montz, a parapsychologist who founded the International Society for Paranormal Research (ISPR) in 1972, also uses the terms “electromagnetic fields” and “corroboration of witnesses” - but to reach entirely different conclusions.

“During paranormal activity, electronic equipment such as video and audio recorders often malfunction,” he says in a recent interview on New Orleans radio. “This type of paranormal phenomena is frequently used by spirit beings attempting to draw attention to themselves. Temperature gauges are also critical, as an entity will usually generate a cold spot. And you have to remember that rooms we investigate aren’t powered - it’s an undisturbed environment - so there’s no unnatural heating but the temperature still drops.”

Dr Montz says that instead of using magnetic field fluctuations to explain why people think they see a ghost or feels its presence, these fields actually prove their very existence. “Lights go off, TVs go on and off by themselves, telephones ring. Entities manipulate electricity, probably because of the electromagnetic fields they generate,” he says.

“Quite often when we go into an investigation all the batteries on our equipment drain for no apparent reason. And you should see the amount of TV shows we’ve done where everything goes down and cameras fail.”

Similar to Dr Watt and the investigation into Hampton Court, Dr Montz has found independent witnesses with no prior knowledge who report the same thing.

“How do I know (that ghosts exist)? The reason we know is because of the experiences that people have had,” he says. “The amazing thing to me as a parapsychologist is the amount of people who have the same experience. They identify the same person and the same phenomenon. They’ll say ‘I don’t know why, but for some reason I just feel there is a little girl standing here’.

Then the next person says ‘I don’t know why but there’s a little girl in here’. It’s just phenomenal.”

But it doesn’t sound particularly scientific - more like hearsay or personal opinion. Dr Montz disagrees. “It is an actual science, like chemistry or biology and so on,” he says. “Our team uses very high-tech thermal cameras, infrared cameras. We also use a device called a magnetometer, which looks like a little voltmeter and measures electromagnetic energy fields. While humans generate electromagnetic fields these are not strong enough to move the instruments, but an entity produces an electromagnetic field strong enough to move the instrument.”

Another sign you’re not alone is inexplicable events, such as car keys being moved from one spot in the house to another. “Quite often when a house is haunted, the entity that remains - and remember these entities are people - wants attention and wants you to know they are there,” Dr Montz explains.

“By moving objects, they just want to be acknowledged, that’s all. Don’t run, just stand in the room and talk to them. Ask them what their name is.

You wouldn’t believe it, but all of a sudden a name pops into your head.

And once you acknowledge them, you’ll probably notice more things going on because they are excited you’ve recognised they are there.” One wonders whether Bobo and Daisy at Powderham Castle would find any comfort in this theory.

* For details of Hampton Court and Edinburgh vaults research, go to: phoenix.herts.ac.ukpwrughosts.html

The Koestler Parapsychology Unit at Edinburgh University: moebius.psy.ed.ac.uk International Society for Paranormal Research: www.ispr.net

A-Z of everything paranormal: www.paranormality.com To hunt your own ghosts, go to: ghosthunterstore.com