Members from Ordnance Survey, Diamond Light Source, the Ministry of Defence, BT, Department of Health, National Grid and the Highways Agency were among those who turned out.
TUC general secretary Frances O'Grady said workers faced the tightest squeeze on their living standards in a century. "Family budgets are at breaking point, real wages are lower than a decade ago and a generation of young people are going to end up worse off than their parents.
"Next month – as multimillionaire bankers get a massive tax cut – ordinary families will be made to pay the price in the form of the child benefit freeze, tax credit cuts and the bedroom tax, all of which will combine with stagnant wages, rising prices and public service cuts to devastating effect."
She drew attention to TUC-commissioned research showing that government welfare and tax changes, together with lower-than-forecast wage growth, would leave nine in ten households worse off by the next election, and half of all children living in families below the breadline by 2015.
O'Grady also called for a fair tax system, a Robin Hood Tax on the banks, wealth taxes on the super-rich and an end to tax avoidance by big corporations.
"Next Wednesday George Osborne should admit that he's got it wrong. The time has come to change course and use the budget not to enrich the City, but to help ordinary families, to bin austerity and promote growth and jobs."
Kate Green, shadow minister for equalities, said 76 per cent of cuts had been felt by women through the loss of public sector jobs and child poverty.
Dwayne Foster, 21, from Dudley, appealed to Osborne to think about the impact of his policies on unemployed young people. He had a B.Tech but could not get a job. "Employers say I lack experience, but it's hard to get experience when no one will give you a job." He wanted to study psychology at university but couldn't afford the fees.
Ruth Cross, USDAW equalities officer, said low-paid women had done more for the economy than Osborne, and Rob Berkeley, chief executive of the Runnymede Trust, highlighted the disproportionate impact of austerity on black and ethnic minority people.
Mandy Hudson, TUC disabled workers committee, said disabled people were not only being victimised but criminalised. Many cuts are being disguised in the universal credit changes coming into effect in April.
Other speakers included Unison, PCS and NUT general secretaries Dave Prentis, Mark Serwotka and Christine Blower; Unite assistant general secretary Tony Burke; CWU president Beryl Shepherd, Spanish union speaker Paula Guisande Boronat; the Child Poverty Action Group's Alison Garnham; GMB rep and carer Maggie Hughes; plus Ian Leahair from the Fire Brigades Union on plans to close 12 fire stations in London.