Israel is beefing up its mental health services as it prepares for an outbreak of Jerusalem Syndrome, a condition which convinces thousands of tourists they are Jesus or another biblical figure.

It has been estimated about 40,000 people will suffer biblical delusions during their Christmas visit to the Holy Land.

Every year thousands of tourists become so affected by the Holy City's powerful religious icons they are overwhelmed by delusions that they are the reincarnation of Jesus Christ, or one of his disciples.

But 1999 has seen a 100% increase in cases, and experts fear the Book of Revelations' prediction of Jesus' reign in the "second millennium" could spark widespread dementia and confusion.

The syndrome affects around one per cent of visitors - and with four million expected to arrive in Jerusalem over the millennium, 40,000 could be affected.

The most frequent sufferers are British and American visitors.

Helen Davis, from the British-Israeli Public Affairs Centre, said: "It can be a major shift in personality. leading people to think they are Jesus, or Moses or King David. Some of these characters can be seen around the city.

"Sometimes they are quite harmless, or usually quite harmless, but sometimes they need serious treatment."

She added: "The psychiatric treatment in Jerusalem has been beefed up for the millennium simply because of the number of pilgrims who will be coming during the millennium year."

Sufferers wear hotel linen

The syndrome was identified in 1982 by the director of Jerusalem's municipal psychiatric hospital, Dr Yair Bar-El.

Most of those who experience it do so for just a short period, with no need of treatment, but some require psychiatric help.

Sufferers become obsessed with cleanliness, they often begin wearing hotel bedding as imitation biblical garb and start prophesising.

Many have delusions that they are Jesus, Joseph or Mary.

Jerusalem is a target city, because of the effect its powerful imagery has on the minds of seriously religious people.

When they arrive, they are overwhelmed and become mentally disorientated. Just being in the Holy Land tips them over the edge.

Real Messiah would be labelled 'insane'

But what happens if the real Messiah puts in an appearance? It would be highly likely he would be deemed insane.

For the authorities this is a pressing dilemma, known as the Jerusalem Question.

Ms Davis said: "The police tend to be rather cynical and deal with day to day problems rather than religious issues...but that [a true prophet] would be a policing issue of major proportions. Millions believe it, who knows?"

One of the most long-standing case studies is Californian Ernest Moch.

He is now known as Elijah and is convinced that he is a reincarnation of the original Prophet Elijah from the Bible.

He says God called him to this city - and to his destiny here in Jerusalem.

In an interview with the BBC earlier this year Dr Bar El revealed he had treated several Jesus Christs, a Virgin Mary or two, and Samson. The Holy City, he said, attracts the vulnerable.

"Jerusalem is like a magnet that attracts people, some of them mentally ill, some of them with deep religious convictions; strange, rare persons", he said.

"Completely sane people arrive here as normal tourists and here they develop a specific type of Jerusalem Syndrome.

"They come here with an ideal and unconscious image of the holy places in Jerusalem, and when they see the real holy places they can't cope. They develop this psychotic reaction to build a bridge between these different images of Jerusalem", he added.