Some of the leading imams in the UK have issued a fatwa against British Muslims travelling to war zones like Syria and Iraq to join "oppressive and tyrannical" Islamic State.
The fatwa "religiously prohibits" would-be British jihadists from joining "oppressive and tyrannical" Isis, also known as Islamic State.
The imams order all Muslims to oppose Isis's "poisonous ideology", especially when it is promoted within Britain, the 'Sunday Times' reported.
The fatwa, six senior Islamic scholars from Manchester, Leeds, Birmingham, Leicester and London, says: "British and other EU citizens are bound by their duties to their home countries according to Islamic theology and jurisprudence: it is therefore prohibited (haram) to travel to fight with any side in Syria."?
It was written by Sheik Usama Hasan, a former imam at the Masjid Al-Tawhid Mosque in east London.
The fatwa, the first of its kind issued by British Muslim scholars, follows the elevation of Britain's terror threat from substantial to severe, meaning an attack is "highly likely".
Prime Minister David Cameron is all set to announce plans tomorrow for laws to prevent British jihadists fighting in Iraq and Syria from re-entering Britain.
Passports of UK citizens suspected of terrorist activity will be cancelled.
In a statement to the House of Commons, the Prime Minister will announce legislation to strengthen anti-terror laws and close a loophole that lets British nationals accused of terrorist activity fly home.
It is feared that the number of young Muslims referred to the UK government's counter-radicalisation programme is expected to "more than double" following the publicity about British jihadists in Iraq and Syria.
Whitehall officials say there has been a direct link between online recruitment messages posted by Isis in the past two months and increasingly extreme views expressed by some young Muslims enlisted into Channel, the de-radicalisation scheme.
Channel, which is run by the Association of Chief Police Officers (ACPO), dealt with 1,281 people in 2013-14, up from 748 in the previous year.
ACPO is understood to be seeking more counter-extremism experts, particularly women, to tackle the growing number of young female Muslims expressing support for Isis.