The pregnant Duchess of Cambridge is being stalked by up to 220 fanatics, according to a newspaper report.
The Mirror says a specialist police team and psychiatric nurses from the Fixated Threat Assessment Centre are visiting the most 'high risk' to carry out 'welfare and medication checks' to keep Kate safe as she prepares to give birth, possibly next month.
The figures were released by FTAC for the first time in response to a Freedom of Information request by the newspaper.
Dai Davies, former head of royal protection for the Metropolitan Police, told the Mirror: "They give rise to a greater likelihood of an incident. If you look back through history the greatest threat to the Royal family apart from the IRA has been fixated individuals.
"Prevention is one of the key areas because in about 70 per cent of cases where there have been attacks, the fixated person has indicated before the incident that they are going to do something."
Led by a psychiatrist and a psychologist, the FTAC is made up of nine detectives, three nurses and a community support officer.
Officers believe the best way to stop stalkers getting too close is to monitor them in the community.
They reduce the risk of a violent incident by making sure stalkers have access to mental health services or placed in a secure unit.
The Mirror says approximately 40 per cent of Britain's most dangerous stalkers focus on the Royals.
Many believe they are the true heir to the throne or that royals are either in love with them or possessed by demons.
Buckingham Palace is said to receive around 10,000 letters a year from people with mental illness. Most of them are harmless, but some contain threats, the paper reports.