Boris Johnson has said tougher laws are needed to combat the threat of British extremists who leave to fight for the Islamic State.
Writing in the Daily Telegraph, Mr Johnson said control orders should be brought back immediately for the most serious cases.
The Mayor of London said those who travel to fight for the terrorist group should be stripped of their citizenship - echoing calls from senior Tory MP David Davis.
Johnson said there should be a "swift and minor change to the law" so that there is a "rebuttable presumption" that those who have travelled to Iraq and Syria, without notifying the authorities, have done so for a "terrorist purpose".
Johnson warned that unless Britain acts to "close down" the Islamic State, the "tide of terror will eventually lap at our own front door."
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.