Thousands of activists are expected to attend a May Day rally to pay tribute to the lives of rail union leader Bob Crow and veteran political campaigner Tony Benn.
The traditional May Day event in London, which celebrates workers' achievements, will honour the two men, who died within a few days of each other earlier this year.
Tony Lennon, chief steward of the London May Day Organising Committee, said: "This year's London May Day presents a huge opportunity for the trade unions and the community to both pay tribute to the massive contribution made by Bob Crow and Tony Benn to the fight for workers' rights, and to send out a clear message that the battle goes on."
Mick Cash, acting general secretary of the Rail, Maritime and Transport (RMT) union, said: "RMT branches and regions have been building for a massive turnout on May Day in London in memory of both Bob Crow and Tony Benn under the theme: Don't Mourn - Organise."
The Occupy movement, which is fighting benefit cuts, will target payday loan companies during a demonstration at the end of the May Day rally.