I DON'T spend all my time dealing with ghosts and poltergeists. The phone rings a lot, but usually it's just a priest wanting advice. I really act mainly as a consultant - for instance, a doctor recently rang me to discuss a patient; he said, 'She needs a priest more than a psychiatrist]' I'm the vicar of Brighton, and also the rural dean, so I spend most of my week on my normal duties in the parish. I perform an exorcism maybe five times a year.

Twenty years ago, the Bishop of Southwark asked me if I'd be interested in the ministry of exorcism, as he knew I was interested in the relationship between psychology and theology. I was fascinated. Around 200 clergymen are authorised by their bishops in this field. The Church of England provides a training course which is run by priests and psychiatrists - they tell you how to diagnose the symptoms of paranormal activity and to distinguish between it and a purely psychological disturbance. Most paranormal activity can be explained by science or psychiatry.

Poltergeist activity is a paranormal phenomenon caused by an energy called 'psychokinesis', and is often caused by stress in an adolescent or pre-adolescent. Extreme upset or unhappiness gives off an energy strong enough to move objects around. When I first started this work, I was hit in the back by a jar of Nescafe which came flying out of someone's kitchen. It scared me then, but now I've seen lots of poltergeist activity. Most recently I visited a Muslim Punjabi family where clocks were zooming around backwards and water was coming down the walls. They consulted me directly - they didn't want to contact their Imam. In such cases they often say that because they are living in a Christian country, the spirits or 'genies' are Christian.

I discovered that they had a daughter who was extremely disturbed by the divided lifestyle she was living; dressing and living the Western way at school by day and being expected to dress and speak Punjabi at home - then her father arranged a marriage for her. It was causing her extreme stress and generating energy that was making objects in the house do odd things.

After counselling, the poltergeist activity stopped.

Ghosts too are usually just manifestations of an unsettled unconscious mind.

Over 90 per cent of all ghost sightings are psychological projections or a bereavement reaction. Often people see the ghosts of dead loved ones because they have a deep inner desire to see them again. Usually the correct counselling will prevent these projections from continuing.

The others are due to genuine paranormal activity. They can be 'place memories' which are like video replays of past human activity, which can be re-energised by a traumatic event. Nothing can be done to erase a place memory. Or the ghost can be an unrested soul - in which case a requiem mass must then be said wherever the ghost is, to lay it to rest.

Possession brings up a theological question. Are the demons part of a person's complex inner make-up and already inside the person's mind? Or has the person been attacked or invaded by an exterior evil spiritual force?

There's a saying that you don't catch a demon like you catch a cold: you have to actually invite one into your life, which happens with people who tamper with satanism. I do believe that there is a force of evil at work in the world. Nazism, Bosnia, South Africa are good examples of it on a political level. But it can also happen to individuals.

Possession happens when someone has lost their own will and it has been taken over by an evil force. Possessed people look very sad and troubled, and yes, the possession can manifest itself physically. I've seen people with excessive strength and violent reactions and people speaking in different voices or languages. The medical term is 'possession syndrome'.

It's disturbing, rather than frightening, to see someone this ill.

The first thing I do is to work out if the demons are internal or external.

I need to find out as much as possible about the personal history and family background. In both cases, the person would need counselling. If an exorcism is to be performed, it must be done with the utmost care and in accordance with the guidelines set out by the Church. It lasts no longer than 10 minutes. The authority of Christ is used to command the evil to leave the person.

You never know quite how the person will react; often they collapse as they are physically exhausted. Five out of the six people I have exorcised have fully recovered after an exorcism. One woman needed on-going psychotherapy and I believe is much better.

As I spend a lot of time with the person before the exorcism, it's quite tiring for me too. It's like being in a boxing ring or wrestling with something quite dark or evil. But possession is very rare. In fact, in 20 years, I've only personally dealt with six cases. I spend more time talking to reporters about them than actually doing them.

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