The UK’s most senior counter-terrorism officer said “significant progress” is being made in the hunt for James Foley’s killer, while the number of arrests of would-be British jihadists and their supporters has increased fivefold.
Police are appealing to the public to help identify aspiring terrorists after the murder of Foley, an American journalist beheaded by an apparently British-born Islamic State militant, focused attention on extremism in the UK.
Assistant Commissioner Mark Rowley announced that 69 arrests of UK nationals traveling to Syria or Iraq to take part in terrorist activities had taken place in the last six months. The crimes of people traveling to Syria ranged from fundraising for jihadists in Syria to preparing terrorist attacks.
Rowley described it as challenging how the number of dangerous individuals has risen, as nearly half of those going to Syria were not previously known as being potential terrorists.
London and the West Midlands have seen the biggest growth in Syria-related investigations.
Intelligence and security agencies in the UK and US are said to be close to identifying the man who is the suspected executioner of Foley in a video broadcast by the Islamic State terrorist group.
Specialists in America claimed to have produced the first possible images of the murderer using computer technology.
Only the eyes of the killer can be seen under a hood, but ABC News has broadcast possible full facial images created by experts.
The murder, believed to have taken place in Syria, reignited a debate over the level of involvement by young British extremists in the conflict there and in Iraq, as well as the risk they pose if they return home.
Rowley urged the public and communities to “help identify for us aspiring terrorists – they may be about to travel abroad, have just returned or be showing signs of becoming radicalized."
He asked for people to watch out for any suspicious change in behaviour, such as selling their possessions or raising money to travel abroad.
He added, "We need everyone to ensure that public debate does not give oxygen to the terrorists by giving them the publicity they seek."
The UK's most senior police officer has said he backs a call to seize passports from Britons who go abroad to fight with militants in Syria and Iraq.
Sir Bernard Hogan-Howe told LBC radio on Wednesday that anything which "stops them from going or... from coming back is a good idea” and suggested that people with "allegiance to a terrorist state" should lose their citizenship.
Hogan-Hove was asked if he would support calls for passports to be taken away from the estimated 500-600 Britons thought to have travelled abroad to fight with the IS.
"If it works, we should do that,” he said. “It seems to me it's a privilege to have a passport and be a citizen of this country, and if you're going to start fighting in another country on behalf of another state, or against another state, it seems to me that you've made a choice about where you what to be."
On Monday, London Mayor Boris Johnson proposed an immediate change in the law to bring in a “rebuttable assumption” that people travelling to war zones without telling the authorities have done so for “terrorist purposes.” He also called for such militants to be stripped of their citizenship, despite warnings from ministers that such a move would be illegal.
Number 10 said Prime Minister David Cameron was focused on a "patient and resolute" response to the "generational challenge" posed by IS. Cameron’s spokeswoman said: "People who insist on travelling to Syria and Iraq will be investigated by the police and the security services. In certain circumstances the home secretary can now remove citizenship from naturalised Britons." The spokeswoman ruled out that Brits travelling to Syria and Iraq will automatically be treated as potential Islamic State terrorists.
She also denied that there would be another attempt to bring in the “snooper’s charter,” which would give the government the power to monitor emails and internet use.
Ten people a month are being stopped from travelling to Syria or Iraq by being referred to the government's anti-terrorism Prevent program, which aims to "stop people becoming terrorists or supporting terrorism."
Meanwhile, the Muslim Council of Britain's deputy secretary general has said the Prevent strategy is having a "negative impact." The scheme seeks to lessen the influence of extremism but Harun Khan told BBC Radio 5 it alienated young Muslims and pushed them towards radical groups.
Scotland Yard is also removing about 800 pieces of terrorist content linked to Syria and Iraq removed from websites including YouTube, Facebook and Twitter.
In the last four years, more than 40,000 pieces of extremist content have been taken down.