Thousands of people, including politicians, union leaders and celebrities, will join a protest against the Government's austerity measures and cuts in public spending.
The demonstration in London today has been organised by the People's Assembly campaign group to highlight the impact on communities and workers of the coalition's cuts.
Spokeswoman Clare Solomon said: "It is essential for the welfare of millions of people that we stop austerity and halt this coalition government dead in its tracks before it does lasting damage to people's lives and our public services."
Comedian Russell Brand, who is supporting the protest, said: "Austerity means keeping all the money among people who have loads of it. This is the biggest problem we face today - all other problems radiate from this toxic swindle.
"We can organise a fairer, more just society than they can. these demonstrations are the start."
Activists from the Stop The War Coalition and CND will join the demonstration.
Sam Fairburn, national secretary of the People's Assembly, added: "Cuts are killing people and destroying cherished public services which have served generations."
A march will start from the BBC headquarters in central London and finish in Parliament Square.
The protest will be followed by a comedy benefit night next month.