Protesters are planning a 48-hour "climate camp" in London this weekend, Scotland Yard has said.
The Met said the London branch of the Camp for Climate Action has informed it of plans for a camp this weekend, including a list of four boroughs protesters may go to, but has not told officers where exactly the site will be.
The camp will be held in the capital in the wake of a separate demonstration by environmental campaigners, aid agencies, politicians and faith groups calling for a strong deal to tackle global warming at crunch UN talks in Copenhagen next week.
The Camp for Climate Action, which is laying on a series of coaches to Copenhagen for protesters to travel to the conference, said the "failing" UN talks were planning "false solutions" to global warming such as carbon trading.
Superintendent Julia Pendry said police were disappointed the campers have not said where they will be.
"Without knowing the location in advance, we can't work with the local authority or local community to help plan for the potential impact of hundreds of people camping on their doorstep for 48 hours.
"We also need to know so we can provide an entirely proportionate policing response to the demonstration, and minimise the potential impact on Londoners who don't want to suffer disruption," she said.
This weekend's event follows a week-long camp at Blackheath in the summer, the location of which organisers kept secret until the last moment and which passed off peacefully - unlike protests against G20 talks in London in April.
The Met Police is holding an international conference on Thursday at Wembley Stadium to discuss policing protests such as these.