Radical Muslims are demanding the security services allow them to leave Britain to live under Sharia law in parts of Syria and Iraq controlled by the Islamic State, so why can't they leave?

Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.

In Walthamstow, east London, a group of young radical Muslims has become infamous for staging 'Shariah patrols' and preaching its hardline take on the Koran.

However, now members of the group say they should be allowed to renounce their British passports and be given safe passage to the caliphate declared by the Islamic State, formerly known as Isis.

This week pro-IS leaflets handed out in central London provoked outrage. They said: "The Khilafah (caliphate) has been re-established...Muslims with the help of Allah have announced the re-establishemnt of the Khilafah and appointed an Imam as a a Khaleef."

Radical preacher Anjem Choudary has claimed the leaflets were the work of his students, though notes he did not produce them.

Channel 4 News met Abu Rumaysah, who was a leading member of the Shariah Project and Muslims against Crusades groups. He says the security services should allow him and his fellow radical Muslims to renounce their citizenship and leave Britain for the caliphate.