Last year's May Day protests were mainly peaceful
Michael Todd, Assistant Metropolitan Police Commissioner, announced up to 6,000 officers would be deployed on the day - a similar number to last year, when 10,000 protesters effectively shut down London's largest shopping district.
Detectives believe a "hard core" of 300 to 400 protesters intent on violence could be active in London during the demonstrations planned for 1 May.
They have identified the wealthy area of Mayfair as a potential target for trouble, after finding a number of internet sites urging protesters to head there.
Mr Todd said: "We do still have very real fears about hard core protesters.
"There is a hard core of people who think the way to get their point across is to cause violence and damage."
But he insisted there would be sufficient officers and expertise "to deal with whatever occurs", and said he remained "optimistic" about the day's events.
'Optimistic'
Last year, police held thousands of people in Oxford Circus for several hours and 100 people were arrested.
The Met believes activists are less organised this year and says the number of pre-advertised actions appears to be small.
It is not advising local businesses to close for the day.
Mr Todd, who will be in charge of police operations over what is expected to be a week of demonstrations and direct action, said he recognised the right to protest.
"The vast majority of people who want to protest want to do so peacefully.
"We understand people care very deeply about certain issues about globalisation and we understand that but we do want to make sure people work with us".
But he warned those seeking to break the law that they would be arrested, adding that police would use "whatever tactics we need".
"Criminal activity will not be accepted by us and will not go unchallenged," he said.
Although he had "some concerns" that protesters might become violent, he declined to provide specific evidence of any plans by activists to do so.
The Met's low-key approach can be contrasted with the run-up to last year's protests, when stories appeared in the media warning of machete-wielding thugs intent on terrorising central London.
Mr Todd defended the controversial tactics used by the Met last year, when several bystanders were caught up in the protests and held for several hours without access to food or toilet facilities.
'Lessons learnt'
But he admitted the force had "learnt lessons" from the experience.
Mr Todd's plea to groups co-ordinating May Day protests to contact police is likely to go unheeded.
One anti-capitalist website urges those planning to take part in the day's actions to "keep moving and don't let the cops surround you.
"This way our festivities will not be crushed."
As well as the main action scheduled for central London on 1 May, protesters have organised a wide-range of activities throughout the week including mass bike rides, workshops, picnics and film screenings.