People could die at west London's Notting Hill carnival if the route is not changed, a report has warned.
Plans to end the route in Hyde Park have been criticised
The mayor's carnival strategic review group said increasing numbers and safety concerns mean one of Europe's biggest street festivals has to change.
It wants the course re-routed through Hyde Park, Bayswater Road and Harrow Road for 2005.
But review committee member Angie Bray condemned the report's findings as "scaremongering".
The 18-month review has looked at ways to boost safety at the 40-year-old festival which takes places over the August Bank Holiday weekend.
"Every year there is not a fatality is a year we have been lucky," Mayor of London Ken Livingstone said.
"We cannot honestly say to people who come to carnival that they are as safe as they could be."
The report stated: "Without a fundamental change to increase public safety and reduce crowd density, a major incident at carnival could lead to significant loss of life."
But review committee member Angie Bray condemned the report's findings and the mayor's "bullying and hectoring tone".
"No-one can say hand on heart there will be no casualties, but that does not mean that this is at an emergency state," she said.
Alan Bradley, of Westminster Council, said: "We would be totally opposed to the procession finishing in Hyde Park.
"We would have huge safety reservations about the use of the park after dusk. The idea of having people in an unlit park would be hugely unsafe."
If the boroughs of Kensington and Chelsea and Westminster do not agree to alter the route, Mr Livingstone said he would call on Metropolitan Police Commissioner Sir John Stevens to use his powers to change it.