They predict the figure will continue to rise as the condition, described as "Pre-Millennial Tension", becomes more acute as 31 December approaches, with the danger of increased suicide rates and family distress.
Fear of technological chaos caused by the millennium bug - the danger that some computer programs, especially older ones, might fail when the date changes to 2000 - and religious associations of the year 2000 with an apocalyptic event are the main reasons.
Fundamentalist Christians, for whom the apocalypse is a firmly entrenched belief, and members of extreme cults are most at risk, but secular people are also suffering severe depression and anxiety because of the warnings of possible technological collapse.
The syndrome is confined mostly to the Christian world - for Jews, Muslims, Hindus and other faiths the year 2000 has no significance - but not just to the United Kingdom. The problems are acute in countries with mass associations of strict religious groups, such as the United States and countries subject to rapid social change, such as Russia and other Eastern European nations. China is thought to have some 200 million evangelical Christians while the Venezuelan government is talking to psychologists and psychiatrists about the millennium bug "in order to know how to reach people in the right manner".
Cults and extreme religious sects have been predicting an apocalyptic conclusion to the 20th century for some time. In 1993, Branch Davidian leader David Koresh was killed together with 80 followers in a shoot-out at Waco, Texas, while 12 people were killed when the doomsday cult Aum Shinri Kyo launched a sarin nerve-gas attack in Tokyo in 1995. Similar problems occurred 1,000 years ago, with debates within Christian and druid circles about whether the world would come to an end either on or around the 1,000th anniversary of Christ's birth.
"It doesn't matter if something isn't really going to happen," said Martyn Shrewsbury, a psychotherapist based in Swansea, who has seen the number of clients suffering from Pre-Millennial Tension double since Christmas. "If enough people really do believe it's true then they'll act as if it is."
Mr Shrewsbury receives up to 25 calls a week and treats 10 patients a month. Some are from members of strict religious sects brought up with a firm belief in judgement day, but many are people with no religious leanings who have "difficulty" with coping with the concept of 2000. He predicts an increase in suicides and greater domestic tension within families before the end of the year.
"For the religious groups, and others, all the ingredients are here right now," he said. "There have been predictions of business failures attributable to the millennium bug. We've heard that health authorities and the police are cancelling all leave for the period. If you are vulnerable and stressed then all these things happening together may push you over the edge. "
The cultural implications of the date 2000 may worry otherwise rational people, said Mr Shrewsbury. "It's a date that has always fascinated everyone. We worry that underneath it all that if the technology goes up in 2000 we'll have to go back to being cavemen and cavewomen."
For many the millennium is merely an outlet for underlying fears, according to Dr Simon Biggs, from the School of Social Relations at Keele University. "People have a lot of irrational concerns about new technology and are anxious about modern life, particularly the casualisation of labour," he said.
"The millennium is a hook which you can hang your anxieties on. People who have anxiety about change and uncertainty in the world can associate closely with the millennium. In some ways if we didn't have the millennium bug as a potential vehicle for disaster we may have had to invent it."
But Dr Sandra Scott, senior psychiatrist at the Maudsley Hospital in London, warned of the danger of creating a self-fulfilling prophecy. "New Year is always an emotive time and this will multiply that effect by a thousand," she said. "Significant events will always be woven into psychosis but if people are constantly reminded of what may happen it can add to the problems. "
The Jehovah's Witnesses - formed in the expectation that the end of the world was due in 1914 - appear to be unfazed by the impending millennium. "We do believe the world system will come to an end but not necessarily in the year 2000. Jehovah's Witness businessmen are probably worried about their computers crashing," said a spokesman for the sect.Reuse content