London - British police face an "unprecedented challenge" from protest groups planning to disrupt the summit of Group of 20 (G20) leaders in London early next month, the officer in charge said Friday.

Commander Bob Broadhurst said 2,500 officers would be deployed to stop environmental and anarchist protestors from bringing the centre of London to a "standstill," as they had vowed to do.

The police operation was expected to cost up to 10 million pounds (14.4 million dollars), he predicted.

"Clearly there are some very innovative and clever people and they know our tactics," said Broadhurst. However, he could not say how many protestors would descend on London.

The summit itself takes place in a conference centre in the former docklands in east London on April 2, but international leaders, including US President Barack Obama, are scheduled to arrive from March 31.

Broadhurst said the main protests in the centre of London and in the City, its financial district, were planned for April 1. (dpa)