Organisers believe it will prevent clashes seen in previous years
Three men have been arrested in a bid to stop troublemakers going to this year's Notting Hill Carnival.
They were held on suspicion of possessing class C drugs after three addresses were searched in Tower Hamlets, east London, on Tuesday.
A hunting knife and what is believed to be a quantity of class C drugs were also recovered, police said.
About 1.5 million people are expected at the west London street party which will take place on 24 and 25 August.
The arrests are part of Operation Razorback, an intelligence led initiative which has been running since 2001 and tries to prevent criminals attending the carnival.
Two more addresses were raided by police on Wednesday in Greenwich, south-east London and Ilford in east London and two men have been given warnings for possession of class C drugs.
More than 100 letters will also be hand delivered over the next few days warning people police know who they are and that they are not welcome at carnival.
Police will also be using metal-detecting arches
Deputy Assistant Commissioner Chris Allison said: "Razorback is all about deterring and disrupting criminals from going along to this year's Carnival.
"Using intelligence we're taken action now to stop this small minority from having the chance to mar this great event for the thousands who attend.
"We've got more people that we're looking at and there will be more arrests over the coming days. Our aim is to create as hostile an environment as possible for criminals."
Metal-detecting arches will be in place at the carnival in an attempt to prevent people carrying weapons.
Officers will also be on the lookout for dangerous dogs after concerns were raised by organisers last year.