Sir Bernard Hogan-Howe, the country's most senior police officer, has urged the Government to increase funding to help the Metropolitan Police catch terrorists and also suggested stripping would-be jihadis of their passports.
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.
"I think we're going to have to look at the resourcing of it, within the Met or across the country," he told LBC. "I know the Australians have just invested an awful lot of money in the same problem in their security services."
"This is a matter for Government, but I think we are going to have to look at it," he added.
He also said that British jihadis who travel abroad to fight for Islamic State should forfeit their passports.
"It seems to me it's a privilege to have a passport and be a citizen of this country," he said. "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."
A British family have told ITV News of their devastation after discovering a close relative is fighting with the Islamic State in Iraq.
A French journalist who was held hostage with James Foley in Syria has told ITV News it was "devastating" to see his murder.