Colleagues of Peter Royal have to be careful not to embellish the tales they tell him of their operations; nurses must clear the decks when (rarely) he has an injection, and a trip to the dentist can be an ordeal both for him and the staff: will he, or won't he?

'I have an almost abject fear of injections, whether they are dental anaesthetics, blood samples or inoculations and they cause me to become dizzy and pass out,' says Mr Royal, a 45-year-old quantity surveyor.

'I have managed to control things a little, but I still come close to fainting if I'm not careful.' When his family doctor showed him detailed photographs of what would happen during his vasectomy operation, he collapsed. 'He asked me if I knew it was going to happen, and strangely I don't think I did,' says Mr Royal.

With Mr Royal it is just needles that trigger the fainting. He believes it is the anticipation of pain that makes him 'shut down'. With Debbie Williams-Conley it is blood - and her problem, which began eight years ago, was compounded because she struggled to cope as a nurse. 'It happened quite regularly when people were having injections into the vein, so I avoided that situation. I could give injections into muscles, but not veins, which fortunately as a nurse you don't generally do. An added anxiety was that as a nurse I was expected not to faint - I was the one who was supposed to be in control.' She is now a behavioural psychotherapist treating people with phobias.

Researchers say blood, needle and injury phobias are extremely common and thought to affect 3.1 per cent of the adult population - around 1.4 million people. Some have all three; others, like Mr Royal, are just phobic about one.

While most phobics are women, blood, needle and injury phobias affect men and women equally. Sufferers range from those who have to steel themselves to visit the dentist to those who even perform the extractions themselves. Harold Fisher, of the Manchester-based Phobics Society, says he has come across three men who have extracted their own teeth rather than visit a dentist.

Many are terrified of hospital investigations and procedures and some would rather suffer - and in some instances put their lives at risk - than expose themselves to the feared object. Some faint in the street if they overhear the words 'needle' or 'blood', though this is rare. Others spend their lives avoiding Casualty and late-night news bulletins. Hard-core cases have their newspapers vetted by friends.

'I've seen women who wouldn't have a baby even though they wanted a family because of what that would involve in terms of needles and blood,' says Jane Wardle, a clinical psychologist at the Institute of Psychiatry.

'There are people who won't travel abroad, even for work. I've even seen someone who always fainted if her children injured themselves and consequently had to have someone with her all the time in case one of her children had an accident. She was an instant and out-cold fainter as soon as she saw any glimpse of an injury.'

Blood, needle and injury phobias are the only ones associated with fainting. When confronted with the feared object, the heart rate quickens and the blood pressure rises, then both plummet. The heart slows down and often stops beating for several seconds. The veins dilate and blood collects in the leg muscles, starving the brain of oxygen.

In some people it happens gradually - Ms Williams-Conley can feel a faint coming on; in others there is virtually no warning.

'All the other phobias are associated with the opposite - the cardiovascular system gets hyped up rather than down. Someone who is terrified of mice or spiders will never faint,' explains Dr Wardle. 'But fainters aren't blindly terrified - they are disgusted or repulsed by the blood. Their reported fear is not nearly as high as with other phobias.'

Children do not generally faint before the age of six or seven and researchers have found that the first faint comes out of the blue. 'It usually involves a child who is interested in the fact that a class-mate has cut himself and is looking on. The next thing they know is that they have fainted and someone is trying to bring them round,' says Dr Wardle.

Psychologists believe that blood, injury and needle phobias are a familial trait and there is increasing evidence to show that such people have cardiovascular systems that make them go into this state more readily than others. Both Mr Royal's daughter and Ms Williams-Conley's father faint at the sight of blood.

'It may well be something that is inherited,' says Dr Wardle. 'There is certainly a higher prevalence of fainting in parents of fainters than in parents of people who don't faint. And it is unlikely to be learnt behaviour; parents will try to keep it from their children because they think their children might copy it.'

But Stephen Wright, a clinical health psychologist at Leicester General Hospital, says that while someone may inherit a tendency to be anxious, a traumatic episode can be the trigger.

'It's all to do with someone's thinking patterns around blood, needles and injury. Those can be made traumatic by a bad experience - or by just not having had any experience and therefore giving them the scope to catastrophise.'

Whatever the cause, the standard treatment is gradually exposing the person to the feared object - first a drawing of a pool of blood, or a syringe without a needle, then a realistic photograph, then encouraging the patient to inject an orange, then watching someone give blood. The final hurdle is to have a blood sample taken. In nine out of 10 cases it works.

To help fainters, psychologists also recommend that they clench the muscles of their arms, legs and buttocks to pump blood back to the heart and brain.

'People do quite well with this technique and they are able to watch operations and so forth,' explains Andrew Steptoe, professor of psychology at St George's Hospital in south London.

Blood, injury and needle phobias decline with age, simply because we are forced to face up to the necessity of syringes and giving the occasional phial of blood. By the time most people reach an age when injections and blood tests are inevitable, the majority have become blase enough to turn away, proffer an arm and sigh.

The Phobics Society, 4 Cheltenham Road, Chorlton cum Hardy, Manchester MZ1 1QN.

Phobic Action, Claybury Grounds, Manor Road, Woodford Green, Essex 1GB 8PL. Hotline: 0452 856021.