Daniel Freeman, a consultant clinical psychologist, was queuing in the post office recently when he overheard a couple discussing the slight discrepancy between two clocks above the counter. "They're trying to confuse us," said the woman. "Yeah," replied the man, "that's typical of the government."
If the couple had noticed the man behind them in the dark suit scribbling down their subsequent conversation ("Now they're trying to stop us living so long and discovering the truth by making us eat genetically modified food"), they might well have hastened home, their conviction about government conspiracy more deeply entrenched. However, the eavesdropper was, in fact, one of the world's leading experts on paranoia. "Some people," says Freeman, "have become so cynical that they don't believe in anything any more. In them, healthy scepticism has been replaced by a total breakdown in trust, the belief that everybody lies. The post office encounter was a fascinating example of that."
Freeman is talking in his small office, lined with books (subjects ranging from binge-eating to ME to sexual and gender identity), at King's College London. He is 37, but has an air of gravitas that makes him initially appear older. He has just written a book, Paranoia: The 21st-Century Fear, with his brother Jason Freeman, a writer. Their thesis is that we are suffering from paranoia more than ever before. It was a mental disorder that was once thought to afflict 1% of the population - basically, people with schizophrenia - but now, according to studies, it affects a quarter of us. Many people with paranoia may not believe - as one of Freeman's patients does - that the government is trying to kill them, or that security agencies have planted cameras in their eyes, but they may worry irrationally that people are gossiping about them, or intend to mug them, or that their children may be taken by paedophiles.
Freeman grew up in Harrow, studied natural sciences at Cambridge and arrived at King's College in the early 90s when paranoia had not yet been the
object of serious scrutiny. "Only the severe end was even considered. There was no sense of spectrum. Paranoia was very much seen as inexplicable, un-understandable, if anything some kind of biological system that had gone wrong. I remember thinking that seemed very reductionalist, that there must be some kind of psychology to it. Once I started looking at it as a spectrum, once you make the connection to things such as depression and anxiety, it really opens it up. People with depression have higher levels of paranoia because of a sense of vulnerability and low self-esteem," he says.
"Anxiety is linked too. But whereas anxiety may lead to fearing harm from a spider, or of being humiliated in a social situation, it doesn't lead to a belief that the spider or others intend to humiliate or hurt us. It's the attribution of intent that distinguishes paranoia."
Over the last 15 years, as a research fellow for the Wellcome Trust, Freeman has found links between paranoia and urbanisation, globalisation, migration and wealth inequality, increased power of the media, CCTV cameras and the internet. Urbanisation particularly fascinates him. "You go into Camberwell [home to King's College hospital] and it's stressful, it's noisy, it's chaotic. You are bustled about, you have to negotiate your path. Sometimes it's familiar and fine, but as soon as you have a suspicious thought, there is ambiguity and confusion, and paranoia thrives in that sort of environment. But it's hard to quantify. We are speculating. There are a number of really consistent results looking at the adult population in Sweden, showing people in urban areas have higher levels of paranoia. But we don't know exactly why," he says.
An environmental or social influence, however, is nothing without a psychological reaction. "This is another main reason why I believe paranoia is on the increase. Because we are constantly reminded, in the press, of threats from other people, we overestimate the chances of these events happening to us. There is a lot of research on this. It is what is known as the 'availability heuristic'. We make an estimate of the likelihood of a particular event simply by how easily we bring it to mind. Our children are getting fat because we aren't letting them out to play enough. We're scared they will be run over or abducted by strangers. In fact, the risks to the health from obesity are much higher than the risks of either of those events."
This is an example of a general paranoia - which many of us may experience. In other cases, paranoia, like depression and anxiety, can cause great anguish. "It's a hierarchy of fear. It's very common to think people are trying to irritate, or upset you. Less so is thinking there are coded negative messages about you in the press and radio.
Paranoia rises in your teens and 20s, drops off and then kicks in again in old age, when debilitation and hearing issues have an effect. But there is a great reticence about it. Go into a bookshop and there are loads of books on anxiety, on depression." He gestures to his own shelves. "Nothing on paranoia."
In all cases, Freeman recommends cognitive behavioural therapy as treatment. We have already established that I am low on the paranoia spectrum. None the less, could he give me a little bit of prophylactic CBT for the future just in case?
He smiles gamely. "The trick is: thoughts aren't facts. Think through explanations for events. We have something called a 'confirmation bias' so that we find evidence to support our bad thoughts. You need to find evidence that goes against them. Finally, if you have a scary thought and you have considered it and think it is unlikely, test it out. I treated a woman who feared the local schoolchildren wanted to attack her. We took her to the school gate as they were coming out. It was brilliant how it worked - watching her face change dramatically when they ignored her.
"Which was lucky," he adds, thoughtfully. "Because I suppose they might have bashed into her."
• Paranoia: The 21st-Century Fear, by Daniel Freeman and Jason Freeman, is published by Oxford University Press.
• This article was amended on Monday 16 March 2009. Daniel Freeman, co-author of a book on paranoia, works at the Institute of Psychiatry, a school of King's College London, not King's College Hospital. This has been corrected.
