They are there to attend a conference organized by Hizb ut-Tahrir al-Islami (Islamic Liberation Party), a group dedicated to restoring the Caliphate to the Islamic world in the Middle East.
The organisation regards the Caliphate, or Khilafah in Arabic, as the ideal form of government which emerged from Islam 1,400 years ago because it is government according to the laws of God, as set out in the Koran, rather than by laws designed by man.
Its message is radical and non-violent, but many experts see it as ideologically close to violent jihadist groups.
Critics describe it as a secretive, militant and highly organised movement.
And it is banned in most of the Middle East and parts of Europe. ...
Our correspondent says it is questionable as to whether the movement is a global force. The evidence suggests it is a fringe group with a utopian agenda and a skilful command of public relations, he says.