The Metropolitan Police has hired a firm of consultants to help it monitor social networking sites.
The police force says it wants to monitor peoples' perception of the Met, and counter rumours about what the police are doing ahead of this week's Climate Camp, which is due to take place during August bank holiday weekend.
The Met Police is two months into a six-month contact with 6Consulting, which is monitoring sites like Flickr and YouTube.
A spokesman said: "We are not monitoring in a criminal sense, we are looking to use the sites to get our message out there.
"We are monitoring how we are perceived. It's not Big Brother-style monitoring."
He said the monitoring activity was in response to the G20 demonstrations earlier this year, when rumours about the tactics police were using spread round internet via sites like Twitter.
He said: "Sometimes the rumours are accurate, but sometimes things get distorted and it can be a case of Chinese whispers."
The police force has set up a Twitter account specifically for the Climate Camp event at @CO11MetPolice. It says Twitter is useful for tracking and responding to rumours over police tactics and actions during events that attract a lot of protestors.