Thousands of people from across the country have started a march in London in protest at the coalition government's spending cuts.
The Trades Union Congress predicts more than 100,000 people will join the march, to be policed by 4,500 police.
The TUC said it was deploying more than 1,000 stewards to ensure the event remained "family friendly".
Ministers say the cuts are necessary to fix the public finances and critics must come up with an alternative.
More than 600 coaches were provided to take people to London on Saturday morning, and marchers set off at 1145 GMT from Victoria Embankment.
They are walking to Hyde Park for a rally from 1330 GMT where speakers will include Labour leader Ed Miliband.
The BBC's Sophie Long, who is with the marchers, says there is "the atmosphere of a festival, with bands playing".
Tax evasion
One of those protesting was Peter Keats, 54, from Lowestoft, Suffolk, who works for Jobcentre Plus.
He said: "Personally, I think it's wrong the way we are hitting the poor.
"I'm not so much worried about myself but the customers I deal with are vulnerable and I'm worried about them and I'm worried about the kids of this country".
Unison general secretary Dave Prentis joined the marchers gathering on Victoria Embankment.
"It's going to be an absolutely incredible demonstration of ordinary working people, and ordinary families, saying this coaliton has got to stop cutting jobs and public services," he said.
The largest union involved, Unite, said so many of its members wanted to take part that it could not find enough coaches or trains to ferry them to London.
Its general secretary Len McCluskey said the scale of the deficit had been exaggerated.
Outlining his economic plan, he said: "Our alternative is to concentrate on economic growth through tax fairness so, for example, if the government was brave enough, it would tackle the tax avoidance that robs the British taxpayer of a minimum of £25bn a year".
Education Secretary Michael Gove said he could understand the disquiet and anger.
"But the difficulty that we have as the government inheriting a terrible economic mess is that we have to take steps to bring the public finances back into balance," he said.
Mr Miliband is attending the march but is yet to sketch out an alternative, he added.
On Friday, the Labour leader said that "the voices of the mainstream majority" would be making themselves heard.
"I think the government will be making a great mistake if they somehow dismiss all of the people on that march as troublemakers, or just 'the same old people'. They are not," he added.
There are some concerns about disorder at the event, and a number of groups have been using the internet to call for the occupation of buildings in the West End.
The Metropolitan Police said it planned to station officers at certain sites thought likely be at risk, such as the Treasury and the entrance to Downing Street.
It has also written to businesses asking them to step up their security and to clear away any loose equipment such as ladders and dustbins that could be used as weapons. BBC News
