British Telecom has been keeping records since it set up its Malicious Calls Bureau two years ago. Last year 15 million such calls were reported to the bureau and 1,500 offenders were prosecuted under the 1984 Telecommunications Act, which carries a pounds 1,000 maximum fine. In addition, the Government's Criminal Justice Bill seeks stiffer penalties for telephone 'abusers'.
Given that calls can be traced and offenders prosecuted, it may seem strange that people persist in making nuisance calls. So, are those who ring up to breathe heavily, talk obscenely - or say nothing at all - in the grip of some kind of obsession? Psychologists tend to think not.
Dr Dorothy Rowe, a psychologist and author, argues that silent callers may be seeking reassurance. 'They may want to be sure that the person they are calling is safe at home or at the place they expect them to be. Sometimes people do that when they are under a great deal of stress and see this person as the only fixed figure in their life.
'When you are really down you often don't want to bother someone, you can't make conversation, but just hearing someone answer the phone reassures you they exist.' But there are callers filled with hate who wish to harm the person they are calling, she says. In between, the feelings behind a call may be more complex than a simple desire to get back at someone who has hurt or rejected the caller, especially when no words are spoken.
'A lot of people make these kind of calls because they feel so helpless. A wife whose husband has left her may be unable to bring herself to speak because she is so upset, yet at the same time she wants to know where he is or who he is with.
'People who make silent phone calls are not suffering from an illness. It can be a way of passing on a message while trying not to take responsibility for it. When the caller knows the person they are calling it can be a way of attracting attention,' Dr Rowe said.
Dr Paul Salkovskis, a specialist in obsessive compulsive disorder (OCD) at Warneford Hospital, Oxford, agrees that nuisance calling is not a disorder. 'Obsessive, used in its everyday sense, is more like enthusiasm. It has a positive angle. People get a buzz out of having every record Madonna has ever made, or whatever. It may become a problem for those around them - but it's very rarely a problem for the people themselves. However, obsessive complusive disorder is different - it seriously messes up people's lives.
'Patients who have OCD are driven by a sense of guilt and anxiety. They are afraid something will happen unless . . .'
He believes that if callers are really seeking reassurance, they will get it only if they speak to the person they are phoning. 'For instance, some patients are afraid they have done something terrible. They convince themselves that the bump they felt as they drove round a corner was the result of running someone over. They keep phoning the police to see if there have been any accidents reported.
'But in all cases the nature of the obsession means that there will be a conversation, because it's reassurance the patient is seeking.'