The March for the Alternative will be a graphic reminder to ministers that the trade union movement does not intend to stand idly by while the government takes an axe to public services built up over decades.
General secretary Bob Crow said: "No-one should underestimate the importance of this demonstration.
"Our members and others in the trade union movement are determined to make sure we send the right message to the Con-Dem government - that they halt the cuts."
Over 700 coaches and a fleet of charter trains will bring people to London from across Britain, and there appears to be little doubt that this will be the largest demonstration organised by the trade union movement in a generation.
The size of Saturday's march and rally will reflect the scale of the damage inflicted on communities and individuals by the government's programme of vicious cuts and so-called "reforms."
Already some 226,000 council workers have lost their jobs or have been given notice of potential redundancy - this before the real impact of the government's decision to slash nearly 30 per cent from local authority budgets is felt.
The False Economy website has estimated that more than 50,000 jobs will go in the NHS, despite government claims that health spending is protected.
Each of these job losses means poorer services for the public and increased pressures on the staff who remain. Little wonder that a recent survey found that three-quarters of public-sector workers felt morale in their workplace was average or poor.
The government's cuts and top-down reforms have left staff demoralised, insecure and under more pressure than ever.
Beneath the statistics, cuts in public services and benefits are exacting a dreadful individual cost.
False Economy features dozens of testimonies setting out the human cost of the government's reckless approach to deficit reduction.
We as unemployed workers', health-care workers, parents and school governors, teachers alongside public and private-sector workers, and for pensioners to march alongside students.