British extremists who go to fight abroad should be stripped of their passports , the country's most senior police officer has said.
Metropolitan Police Commissioner Sir Bernard Hogan-Howe backed growing calls to take citizenship from aspiring terrorists who go to war zones, although Deputy Prime Minister Nick Clegg has already rejected the idea.
The Scotland Yard chief also called for the return of the abolished control orders, under which terror suspects could be forced to move to another part of the country and placed under a lengthy curfew.
Speaking on LBC, he said: "Certainly for us anything that either stops them from going or preferably stops them from coming back is a good idea. If it works, we should do that.
"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."
Of the estimated 500 or 600 British aspiring terrorists thought to have travelled to Syria, around two-thirds or three quarters are thought to be from London, and Sir Bernard said earlier this month that Scotland Yard is prepared in case a wave of extremists decide to return home at the same time.
He called for the reintroduction of "something like" the abolished control orders for suspects who cannot be charged or deported, which were replaced by less restrictive Terrorism Prevention and Investigation Measures.
"They were stopped because the threat was reduced and quite properly they were seen as too intrusive," Sir Bernard said.
"But I think these things have got to be considered when the drum beat changes, and it's clear that the drum beat has changed."
Earlier this week Mr Johnson used his Daily Telegraph column to say those who "continue to give allegiance to a terrorist state" should lose their British citizenship, and that the law should be changed so there is a "rebuttable presumption" that those visiting war areas without notifying the authorities had done so for a terrorist purpose.
However, during a visit to India, Deputy Prime Minister Nick Clegg rejected calls for tougher measures to combat the threat posed by returning British jihadists.
He said: "We actually have a number of measures already on the statute book which allow us to keep a very close eye on those people who aren't in prison, aren't sentenced, but nonetheless are perceived to be a threat to the United Kingdom.
"And of course, we will continue to review all the powers on the recommendation of the police and security services that may be deemed to be necessary to deal with this very serious issue.
"I sometimes wish it was as simple as Boris Johnson implies: all we need to do is pass a law and everything will be well."
Yesterday Scotland Yard confirmed that "significant progress" is being made in the search for the apparently British murderer of American journalist James Foley, who was beheaded by extremists in Iraq.
Sir Bernard said that the force is working with American counterparts to firmly establish whether the murderer is British, as his accent suggests.
"We are making progress in that investigation, of course we are working with our partners in America because this was an American citizen who was murdered by a British citizen, it appears.
"First of all we have to tie down who we think did it, where it happened, and then we can start talking about jurisdiction.
"Obviously there is a voiceover, which everybody's heard, which sounds like a Brit. It sounds like somebody from London, that's all the experts tell us. So we're investigating whether that's true.
"Our investigation is making progress but it's not straightforward, it's not got a name plate stuck on it. We are going to have to do quite a lot of work with various people to try to get to the bottom of it."
Islamic State terrorists posted a video online last week of the horrifying murder of hostage Mr Foley in Iraq.
Sir Bernard urged members of the public not to watch footage of the killing, out of respect to the 41-year-old's family, and warned that sharing the chilling clip could be a terrorist crime.
"I've seen some of it, I've not seen the awful bit, frankly I don't think I need to, and I'd urge other people not to look at it out of respect for the family. I think it should be avoided," he said.
The Home Office insisted terrorism prevention and investigation measures (Tpims) were a "useful weapon" and had the support of the courts, police and MI5, while the control orders they replaced "were not working".
A spokesman said: "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.
"The police, security services and Border Force are actively working to tackle all terrorist threats. We have a wide range of tools at our disposal to disrupt travel and manage the risk posed by returnees, including powers updated by the Home Secretary to cancel and seize someone's passport.
"Under new powers in the Immigration Act, the Home Secretary can also deprive citizenship from a naturalised British citizen if they have acted in a manner seriously prejudicial to the vital interests of the UK. In certain circumstances, this power can be used whether or not the individual is a dual national.
"Tpims are another useful weapon in our armoury. They were introduced because control orders were not working and their powers were being struck down by the courts.
"Our priority is always to prosecute and through the Serious Crime Bill we intend to strengthen the law further to make it a criminal offence to travel overseas to prepare and train for terrorism."
Human rights group Liberty called the removal of citizenship a "wacky and dangerous" new power.
Policy officer Rachel Robinson said: " Citizenship-stripping is a tool of dictators not democrats, a terrible injustice for the innocent and irresponsible to the international community.
"And why is our most senior police officer wading into politics anyway? The police are meant to enforce the law impartially, not lobby for wacky and dangerous new powers."