According to 'The Times', the police have received intelligence inputs that violent protesters could well target the hotels and other buildings where the world leaders would be staying during the summit on April 2.

All police leave has been cancelled in London for the first two days of next month; thousands of uniformed officers will be on the streets to stop street protests; and the number of close protection officers which will be stationed at each location has also been increased, the report said.

However, the police are confident that they can protect the summit venue, the ExCeL Centre, which is bordered by railway lines and docks and is close to an airport. "The protest groups are intent on causing as much disruption to the summit (as possible) but we think that a lot of their talk is aspirational rather than achievable," an unnamed source said.

US President Barack Obama, French President Nicolas Sarkozy, German Chancellor Angela Merkel and Indian Prime Minister Manmohan Singh, among others, are expected to attend the world summit.

In fact, anarchist groups and environmental activists are already collaborating on a series of demonstrations, which are being advertised with slogans such as "Storm the Banks" and "Bash a Banker", the report said.

However, the security operation to protect politicians attending the event will be the "largest seen in Britain since the G8 met at Gleneagles in July 2005".

In addition, though there is no intelligence pointing to a terrorist attack to coincide with G20 summit, the report said that a detailed anti-terrorist contingency plan has been drawn up by the police.

"We could never rule out the idea that the G8 event might have been the inspiration for the 7/7 terrorists. There is no intelligence of an attack now but we would be foolish if we weren't thinking along those lines -- you cannot afford to discount any possibility," the source was quoted as saying.

But, the protest organisers are emphasising the flexibility of their plans and have set up text message alert systems to keep their followers informed of changes in the choice of venue or tactics, the report said.