The comments were broadcast as religious leaders called on British Muslims not to travel to Syria and Iraq, amid fears of terrorists fleeing the country to take part in terrorism.
An open letter signed by more than 100 imams from across major theological backgrounds and cultural groups has urged British Muslim communities "to continue the generous and tireless effort to support all of those affected by the crisis in Syria and unfolding events in Iraq", but to do so from the UK "in a safe and responsible way".
Concerns have also been raised about homegrown involvement in terrorism after Britons appeared in a propaganda video for terrorist group Islamic State in Iraq and the Levant (ISIL).
Among them was aspiring terrorist Aseel Muthana, who told the BBC he was fighting in Syria and had no intention of returning to the UK.
His brother Nasser appeared with two other British men -– 20-year-old Reyaad Khan, from Cardiff, and Abdul Raqib Amin, who grew up in Aberdeen – in an ISIS propaganda video.
BBC5 Live broadcast an interview with a man calling himself Abu Osama, whose accent suggested he comes from the north of England and who claimed to have been fighting for the establishment of a so-called caliphate across the Islamic world.
His claim to have been taking part in military training, making bombs and fighting with the extremist Al-Nusra Front, which is linked to al-Qaida, for the past year has not been verified.
The man told interviewer Nicky Campbell: "I have no intention of coming back to Britain, because I have come to revive the Islamic Khilafah. I don't want to come back to what I have left behind. There is nothing in Britain – it is just pure evil.
"If and when I come back to Britain it will be when this Khilafah – this Islamic State – comes to conquer Britain and I come to raise the black flag of Islam over Downing Street, over Buckingham Palace, over Tower Bridge and over Big Ben."
In April, the Metropolitan police issued a plea for people to come forward with information about their family members if they were concerned about them joining terrorist training camps in Syria.
Qari Mohammed Asim, imam at Leeds Makka Mosque, who played a key role in organizing the letter, said: "The scale of the humanitarian disaster in Syria and the escalating violence in Iraq calls for an unprecedented response.
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