Police say protesters are planning in an "unprecedented" way for London's G20 summit next week. But how do campaigners prepare for a demonstration?
Some Climate Camp members played a familiarisation game in the City
Outside Liverpool Street station in the City of London on a Friday evening in March, a band of young people began to congregate.
They arrived in ones, twos and threes - most aged in their early 20s - and could have been meeting for a regular night on the town.
However, the large presence of police inside and outside the station told a different story.
Many in the group were members of Camp for Climate Action - behind direct action protests at Heathrow airport and power stations in North Yorkshire and Kent - and the authorities are watching them carefully.
The main reason for police company was most likely to have been the organisation's warnings of a day of "spectacular action" at the G20 summit in London next week, when supporters intend to "set up camp" in the City on 1 April.
Earlier that same day, the Metropolitan Police had warned some activists were planning in an "unprecedented" way ahead of the meeting and that there were some "very innovative and clever people" involved in the preparations.
And as darkness fell in Bishopsgate, it soon became clear how seriously the authorities were taking the planned demonstrations as one officer took out a video camera and filmed all those waiting and chatting, close enough to record their faces.
The assembled group had come together to play a game called capture the flag, which Climate Camp members say was designed to help those intending to join the G20 protest to "familiarise themselves with the locale" where they intend to set up their tents.
G20 LONDON SUMMIT
World leaders will meet next week in London to discuss measures to tackle the downturn. See
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The G20 countries are Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, the United Kingdom, the US and the EU.
Once game instructions and maps were handed out and the group was split into two teams, members headed deep into the City followed by a collection of police on foot, horses, motorbikes and in vans.
The task, which saw each team dash around the Square Mile trying to locate the opposition and claim its flag, ended in high spirits and without trouble.
"It's fun. It is reclaiming public space to play in," enthused Mel Evans, one of the players.
Peter McDonnell, a Climate Camp spokesman, said although an "enormous amount of fun" had been had, the event had a practical aim.
"The game was an opportunity for people to familiarise themselves with the area - the geography - so they know what to expect when we have to act quickly," he said.
But Climate Camp's preparation for G20 has gone much further than familiarisation games.
Members have held a day-long seminar on carbon trading policies - the target of their protests - as well as a detailed planning meeting, which included direct action training and legal advice.
Those attending were taught how best to hold and maintain a space, how to defuse confrontational situations as well as how to communicate with the media.
While Climate Camp is a non-violent organisation, some members have shown a willingness to practice civil disobedience to highlight issues surrounding global warming.
"It comes to a point that it is so frightening - how the crisis is looming - I think it necessitates people going a bit further to try to make things happen," said Mr McDonnell.
Professor Wyn Grant, of the University of Warwick, said the meticulous preparation by such groups was part of an "upward learning curve" that had resulted from experience at successive protests.
But, as well as the benefits of such knowledge, what has arguably allowed groups like Climate Camp to co-ordinate large numbers of people in such an effective way is their vast use of digital communication.
"The technology available to organise such protests has improved, notably the mobile phone, but also the internet - Facebook, Twitter," observed Professor Grant. "This facilitates more effective mobilisation."
Climate Camp itself has own website featuring comprehensive instructions and resources, including a downloadable map of potential protest sites, a list of what to take on the day and even a downloadable "bust card" detailing legal rights if a protester is arrested.
Members say they have used Google's online Street View mapping facility for research as well as social networking sites such as Facebook and Twitter - along with those aimed at social movements, such as Crabgrass - to correspond with supporters and share ideas.
But the communication doesn't end there.
Climate Camp protested at Kingsnorth power station in Kent last year
Those wanting to participate in Climate Camp activities can also sign up for a text message news service which will keep them informed of changes in plans before and during the protests.
Yet, while such demonstration groups have shown a high level of sophistication in their preparations, the very public nature of online communication means police have been following them every step of the way.
Commander Simon O'Brien, one of those in charge of next week's G20 policing, has revealed officers have been monitoring social networking sites, describing the process as "key".
"That's where we are picking up a lot of our intelligence about numbers and what certain groups are aiming to achieve," he said.
Yet, while police have been trying to outwit activists online, the promise of civil disobedience next week means they could be forced to outthink them once again on London's streets.