James Foley beheading: Boris Johnson says anyone returning from Iraq and Syria should be arrested

The Mayor of London called for increased legal powers against Isis suspects

London Mayor Boris Johnson speaks at the Confederation of British Industry's (CBI) annual conference on November 19, 2012 in London, England. The United Kingdom's business leaders have gathered at The Grosvenor House Hotel for their yearly one day confere (Peter Macdiarmid/Getty Images)

Anyone attempting to return to the UK from visiting Iraq or Syria “without a good reason” should be classified as a potential terrorist and arrested, Boris Johnson has said.

The Mayor of London, who will be standing as a Tory MP next year, wants the law to be reversed so there is a “rebuttable presumption” of guilt until people are proved innocent.

“Do nothing now, and the tide of terror will eventually lap at our own front door,” he wrote in the Telegraph.

As many as 500 British citizens are believed to be fighting for the Islamic State (Isis) and other terrorist groups in Iraq and Syria, including a former London rapper then known as L Jinny, who is believed to be one of many UK-born terrorists under investigation for the murder of James Foley.

The beheading of the American journalist, recorded in a gruesome propaganda video, appears to have been by a British militant with a London accent nicknamed “jihadi John”, who authorities are close to identifying.

Abdel-Majed Abdel Bary, pictured here in a YouTube video showcasing his rapping as L Jinny, is one of many British suspects believed to be under investigation

Writing in his Telegraph column, Mr Johnson said: "I suspect most of us don’t give a monkey’s what happens to this prat in heaven, whether he meets virgins or raisins – we just want someone to come along with a bunker-buster and effect an introduction as fast as possible."

He argued more needs to be done to prevent foreign extremists travelling to Iraq and Syria, including Turkey shutting the border.

“We need to make it crystal clear that you will be arrested if you go out to Syria or Iraq without a good reason,” he wrote.

“At present the police are finding it very difficult to stop people from simply flying out via Germany, crossing the border, doing their ghastly jihadi tourism, and coming back.

“The police can and do interview the returnees, but it is hard to press charges without evidence.

“The law needs a swift and minor change so that there is a ‘rebuttable presumption’ that all those visiting war areas without notifying the authorities have done so for a terrorist purpose.”

The Mayor reflected concerns aired by the Foreign Secretary, Philip Hammond, that if Isis is taken down, its foreign militants will flee back to their countries of birth and continue their jihad at home.

He urged for the return of Tony Blair’s control orders, scrapped by the Coalition, which could keep terror suspects in their homes without access to phones or the internet.

If known militants fighting with extremist groups choose not to return, he called for the removal of their British citizenship.

The “Isil wackos” – as Mr Johnson dubbed them – control an area the size of the UK across Syria and Iraq, including cities, industry, oil reserves and a population of around six million people.

Their reportedly well-funded military capability sent the Iraqi army fleeing in retreat as Isis went on a bloody rampage through the country earlier this year and countless civilians have died in the Sunni group’s vicious persecution of Shias, Yazidis, Christians and other minorities.

Still scarred by the British involvement in the previous Iraq and Afghanistan war, David Cameron has repeatedly vowed not to put “British boots on the ground”, despite mounting outrage about Isis atrocities and its potential power if its dream caliphate is established.

The Government has not yet joined the US in launching air strikes against militants, instead sending humanitarian aid, working with the Iraqi Government and international security services.

Mr Johnson appeared to support increased intervention in his Telegraph article, saying Isis territory needed to be “closed down now”, before becoming a “giant training ground for terrorists”.

“No option looks very appealing, to put it mildly; and yet doing nothing is surely the worst of all,” he wrote.

“If we let Isil (Isis) get their way, then we will be acquiescing, first, in a gigantic and violent change in international borders…we will be allowing a new and hideous regime to be born.”

Mr Hammond has previously said “significant powers” were already available to deal with people planning to travel to Syria or Iraq to fight including withdrawing passports, monitoring them overseas and arresting them on their return.

“I don’t think this video changes anything,” he told Radio 4. “It just heightens awareness of a situation that is very grave and that we’ve been working on for many months.”

James Brokenshire, the minister for immigration and security, said the Government already has the power to remove citizenship under the Immigration Act and control orders had been ineffective because of legal challenges.

“People seeking to travel to engage in terrorist activity in Syria or Iraq should be in no doubt we will take the strongest possible action to protect our national security, including prosecuting those who break the law," he added.

“The police, security services and Border Force are actively working to identify, detect and disrupt terrorist threats, including from British fighters attempting to return to the UK."