The Home Secretary is to bring in new laws to tackle British extremists, warning that the security threat to the UK will continue "for decades."
In the wake of the horrific execution of American journalist James Foley by a "cowardly" jihadist with an English accent, Theresa May said Britain must introduce all the legal powers necessary to win the struggle against terror.
The jihadist in the execution video, which shows Foley kneeling in the desert with his head shaved and wearing an orange jumpsuit before he is beheaded, is believed to be the ringleader of a group of UK-born extremists, and using the name 'John'. They are apparently responsible for guarding Western hostages in the stronghold of Raqqa, and nicknamed after members of the Beatles, with the two others dubbed Paul and Ringo.
May announced she is planning to bring in new laws including "anti-social behaviour orders" for extremists and banning orders for certain groups in an effort to stop radical preachers, such as Anjem Choudary, whose inflammatory rhetoric currently does not constitute a crime.
As with an Asbo, it is thought the new order - which could target extremists "behaviour and language" - could result in a criminal conviction carrying a jail term if breached.
The new laws would target radical preachers like Anjem Choudary
The Home Secretary also underlined changes to the law that mean naturalised Britons who are fighting overseas can be stripped of their citizenship and excluded.
In an article for The Telegraph, she said: "We will be engaged in this struggle for many years, probably decades. We must give ourselves all the legal powers we need to prevail.
"The cowardly murder this week of James Foley, a man who was working to highlight the suffering of the Syrian people to the world, has demonstrated once again the very deadly threat we face from terrorism at home and abroad," she said.
"I am looking again at the case for new banning orders for extremist groups that fall short of the legal threshold for terrorist proscription, as well as for new civil powers to target extremists who seek to radicalise others."
Journalist James Foley who was executed by IS militants
Footage issued by Islamic State militants that shows 'jihad John'
She added: "People who insist on travelling to fight in Syria and Iraq will be investigated by the police and security services.
"For those who have dual nationality, I have the power to strip them of their citizenship and exclude them from the country.
"Following the recent Immigration Act, I can, in certain circumstances, remove citizenship from naturalised Britons who are fighting overseas and exclude them too.
"And while it is illegal for any country to make its citizens stateless, any British national who returns from Syria and Iraq faces prosecution here for participating in terrorist activities abroad."
But Yvette Cooper, Labour's shadow home secretary, said that although May's new plans are "welcome," "more action is needed to respond to the serious problem of people travelling to fight with Isil."
"There remains no detail on things like civil powers to tackle extremists or extremist groups for people to consider," she said.
"I remain concerned that the Government is not addressing the gaps in the Prevent programme - especially the lack of support for community led approaches to preventing radicalisation.
"And the Home Secretary also needs to respond to the concerns raised by the current and previous Independent Reviewer of Terrorism Legislation about the decision to weaken control orders, where they have advised that stronger measures should be put in place."
Since the coalition came to power in 2010 more than 150 people have been excluded from Britain for "unacceptable behaviour" , including foreign hate preachers.
Police have also secured the removal of 28,000 pieces of terrorist material from the Internet.
The Government has come under pressure to contemplate working with the Assad regime to tackle the militants operating in Syria and Iraq, with former head of the army Lord Dannatt suggesting there was a need to build bridges with the Syrian president.
But Foreign Secretary Philip Hammond said an alliance with the Assad regime would not be "practical, sensible or helpful".
The UK Government has called for Assad to be removed as Syrian leader as a result of his actions during the country's bloody civil war.
Asked if the UK would have to collaborate with the Assad regime, Mr Hammond told BBC Radio 4's World at One: "No. We may very well find that we are fighting, on some occasions, the same people that he is but that doesn't make us his ally."