Beefed-up counter-terrorism tactics are being introduced in the City of London two decades after a "ring of steel" was put in place around the Square Mile.
City of London Police have carried out three years of research looking at the traditional system of manned entry points into the area, brought in as a response to the terror threat in the 1990s.
The force now plans to make greater use of undercover teams, stage less predictable operations and use CCTV and number plate recognition as part of the fight against terrorism as well as other serious crimes.
Assistant Commissioner of City of London Police Ian Dyson said: "The ring of steel worked, it provided a deterrent, but it was getting tired.
"It was single officers standing on entry points, normally at predictable times of the day, which was the rush hour.
"While businesses were very supportive of the uniformed presence, the reality was in terms of intelligence, in terms of the research we did around deterrent, it was proving to be of diminishing value.
"This is about looking at a refreshed opportunity to make the City a hostile environment for anyone who may be seeking to do any sort of criminality, particularly terrorism."
The force launched the refreshed tactics, dubbed Project Servator, with an operation on Tower Bridge this morning.
Mr Dyson added: "The threat level remains the same, but equally London remains a huge global financial centre, it is a target, it will be for a long time, as long as London remains that. Only two years ago there were people arrested for a plot to try to blow up the Stock Exchange, there is always an element of trying to get an iconic or a financially disruptive target."
A range of different teams will be used in the operations, including explosive detection dogs and the mounted branch, and the initiative is being widely publicised.
"We're publicising the fact that we're doing it, significantly," Mr Dyson said.
"We will be publicising as much as we can, so that anyone will know that these operations are being carried out. What they won't know is when and where and for how long.
"It is much more visible at a time of diminishing police resources, hence there's going to be a range of officers on it."
Similar tactics have been used at transport hubs in the capital, and in a trial run by the City of London Police in November and December 2012 officers carried out 208 stops and around one in three led to an arrest, caution or a car being seized.
Around 300,000 people come to work in the area every day and it is estimated that the Square Mile contributes £50.2 billion to the UK economy.
Pedestrians will be stopped and questioned as officers target crowded places, as well as using vehicle checkpoints to stop cars, and operations will be staged every day at different times.
The launch operation today involved more than 20 uniformed officers, with more in plain clothes, and the Metropolitan Police marine support unit.