Militant demonstrators aiming to disrupt next week's G20 summit will use Twitter and text message alerts to stay one step ahead of a massive police operation.

Messages circulating among demonstrators emphasise the importance of being able to keep in contact with each other because protest plans are likely to change minute by minute. One e-mail said: “Things may change on the day, perhaps significantly.” Other messages urge protesters not to bring knives or illegal drugs.

Because the protests pose a threat to public order, rather than to security, police cannot use telephone intercept powers to discover what the demonstrators are planning. One senior officer said: “There is the prospect of us playing cat and mouse around London – trying to stop incidents as they flare up.”

Scotland Yard also hopes that the poor weather that has been forecast for this weekend will continue next week and keep protest numbers low.

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A week of protests surrounding the summit begins today with the Put People First march through Central London to a rally at Hyde Park. Anarchist and direct action activists have been threatening to hijack the event.

Glen Tarman, the chairman of the organising committee, said: “The march for jobs, justice and climate brings together more than 150 groups committed to making the event a peaceful and law-abiding call on the G20 governments to commit to policies that will deliver jobs, end poverty and move to a low-carbon economy.”

He added: “We have no evidence that anyone attending intends to disrupt our plans, break the law or commit any acts of violence.”

The more militant groups are advertising their main protests for Wednesday and Thursday – the eve and day of the G20 meeting. An unprecedented number of protests have been planned for April Fool's Day, when events range from the G20 Meltdown – with calls to storm the banks – to a Stop the War rally outside the US Embassy and an overnight Climate Camp in the heart of the City. Planners of the proposed camp have told their supporters to gather in small groups on the edge of the City and swoop on their target site.

Their e-mail states: “Be aware that in light of current overpolicing tactics, if you miss the swoop, you may be unable to join the camp. In places where our numbers are too low, the police may attempt to stop and search individuals, and confiscate items to prevent us from setting up the camp safely. We can avoid this by moving confidently and together.”

Protest organisers also urged awareness of police tactics, such as “the kettle”, in which large numbers of officers surround groups of demonstrators. The tactic was used to stifle protest on May Day 2001, when thousands of activists were corralled in Oxford Circus.

The next day the focus of protests shifts to East London where a massive security cordon has already been erected around the ExCeL centre, the venue for the meeting of world leaders. All police leave has been cancelled on the two days and 2,500 uniformed officers will be deployed in Central London on Wednesday. The combined cost of the public order and security operations is likely to reach £10 million.

An anthropology professor involved in planning the G20 Meltdown was suspended by his university after speaking in a radio interview about hanging bankers from lampposts. The University of East London confirmed that an investigation had begun into comments by Chris Knight, 66, from Lewisham, southeast London.

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