Extremists can display Isil flags in London because Britain is a "free country", Boris Johnson has suggested.
The Mayor of London said that he does not support the banning of iconography associated with the extremist group.
The man and little girl flying an Isil flag outside Parliament on Saturday (LiveLeak)
Mr Johnson's stance is at odds with David Cameron, who last year insisted that anyone caught flying an Isil flag would be arrested.
It comes just days after police officers allowed a man and a little girl to fly an Isil flag outside Parliament.
Scotland Yard said officers spoke to the man but considered his action to be 'within the law'.
Boris Johnson, the Mayor of London
Mr Johnson, speaking on his weekly LBC radio show, said: "I don't want to see any Isis flags flown triumphantly around London but we live in a free country.
"You would have to have legislation to designate some iconography to be illegal.
"In the London Pride march recently the police did confiscate a flag that they thought was an Isis flag but it turned out not to be.
"You have got to be careful how you approach it."
Britain’s top police officer also appeared on Monday to be on a collision course with the Prime Minister after suggesting that carrying an Islamic State in Iraq and the Levant flag in Britain should not lead to automatic arrest.
Sir Bernard Hogan-Howe, the Commissioner of the Metropolitan Police said carrying the black flag of the terrorist organisation was “not necessarily the worst thing in the world”, adding that the police should not overreact.
Last year, in an article for the Sunday Telegraph, Mr Cameron said: "The position is clear. If people are walking around with Isil flags or trying to recruit people to their terrorist cause they will be arrested and their materials will be seized.
“We are a tolerant people, but no tolerance should allow the room for this sort of poisonous extremism in our country.”
After the most recent incident near Parliament, a spokesman for the Metropolitan police said: “Wearing, carrying or displaying of an emblem or flag, by itself, is not an offence unless the way in which, or the circumstance in which, the emblem is worn, carried or displayed is such as to cause reasonable suspicion that the person is a supporter or member of a proscribed organisation.
“While support of and membership of ISIS is unlawful it is not a criminal offence to advocate the creation of an independent state.”
But a Downing Street spokesman said: “From our perspective the Prime Minister’s comments are clear so we have nothing further to add.”