New London mayor Sadiq Khan said he has ordered an "urgent" review of how ready the city is to tackle a major terror attack because the criminals are always "evolving their tactics".
Mr Khan stressed that public safety and security has to be a top priority, particularly in light of the recent Paris and Brussels attacks, as he announced that former Metropolitan Police Authority chairman Lord Harris will lead the review.
He said: "It is quite clear that terrorists want to attack London. They have attacked Paris. They have attacked Brussels. They have tried to attack London in the past. We have got to make sure we are constantly vigilant.
"I have asked Lord Harris to carry out an urgent independent review to reassure me that our city is prepared for, God forbid, a major terrorist incident."
Mr Khan said he wanted a fresh look at all current arrangements including how the city would cope if multiple terror attacks were launched along with the work and resourcing of all the emergency services to protect Londoners.
He said: "The terrorists are evolving their tactics and we have got to evolve our response to them all the time.
"I am afraid the consequences of a terror attack are very very scary. They want to kill. They want to maim and terrify. It is my job to try to make sure that we are as safe as we can be."
All of the emergency services along with Transport for London, the Port of London Authority and local government representatives will be contacted as part of the review, which is set to release its findings in the summer.
Lord Harris said that London responded well to its July 7 terror attacks but that new tactics are being deployed by terrorists.
"We have seen the marauding attacks rather than people packing explosives on their backs," he said.
Lord Harris also said that a review is "critical" because of the changing nature of the terrorist threat.
He pointed to the bloody four-day siege at the Westgate Shopping Mall in Nairobi, Kenya, in 2013 and the co-ordinated Mumbai hotel terror attacks where 166 people were killed in November 2008.
Lord Harris, who is a former London Assembly member and oversaw the Met's national counter terror strategy for the Home Office, said: "I think we have to assume that London is always a target.
"My understanding, although I have not been briefed on it, is that the threat level is extremely worrying. It is entirely right and proper that the emergency services plan for all possible threats."
Earlier this month, MI5 raised Britain's threat level from Northern Ireland-related terrorism from moderate to substantial for the first time since 2011.
Lord Harris added: "Even if the experience of the Irish-based attacks may seem like a long time ago, we want to make sure that all the lessons from that period have not been lost."
Metropolitan Police Commissioner Sir Bernard Hogan-Howe said: "Although we are confident the Met can deal effectively if terrorists did strike our city, and we test ourselves regularly, we are never complacent about the city's security and recognise that there will always be ways in which we can improve."