The Dutch authorities managed to keep 23 radical Islamic preachers from preaching in the Netherlands since March last year. Eight of them were denied a visa, the other 15 had their invitations to come preach retracted, according to a spokesperson for the National Coordinator of Counterterrorism and Security, Het Parool reports.

According to the spokesperson, the second category is particularly important. The local government starts a discussion with the organizers of a particular event and convinces them not to invite the radical preacher. "Starting the debate is important", the spokesperson said.

The National Coordinator uses an "alert list" of extremist preachers who need a visa to come to the Netherlands. If someone on that list applies for a visa, the authorities check whether he will pose a risk to public order.

But it is more difficult to keep out radical preachers who live in Europe. "As long as someone has not been convicted of a criminal offense, it is not legally permissible or proportionate to put him on a list of 'suspects' and share this list with, for example, the local government", according to the Ministry of Security and Justice. This makes successfully negotiating with event organizers very important.