Ed Miliband suffered outbreaks of heckling today as he addressed tens of thousands of people marching against the coalition's spending cuts.
The Labour leader, who faces a near-impossible balancing act whenever trade union demonstrations take place, refused to go on the march but gave an address at the end of it in which he promised to tax bankers' bonuses, build 100,000 houses and end the privatisation of the NHS.
"David Cameron tried to keep his chief whip, even though the rest of us could see he had to go," he told the crowd.
"He clings to an economic plan that is just not working. David Cameron: a weak, clueless prime minister, who cannot stand up for the interests of this country."
But when the Labour leader spoke of "tough choices" – code for spending cuts if Labour returns to power – there was an outbreak of heckling at the front of the crowd.
Miliband was widely criticised by Conservatives and free market groups for attending the march, which Cameron dubbed "the most lucrative sponsored walk in history" – a reference to the unions' funding of the labour party.
But refusing to attend the rally would have alienated Labour's core supporters and damaged relations with the unions and public service workers.
The 'Future That Works' march followed a nearly three mile route, beginning on the Victoria embankment of the Thames and ending in Hyde Park.
"We have to make a choice between a future of growing inequality or a future of fairness,” TUC general secretary Brendan Barber said.
"The biggest lie of them all was the cynical double talk that 'we are all in this together'."
There was little sign of the violence which marred the last major anti-cuts rally, when anarchists attacked banks and UK Uncut activists were arrested en masse following an occupation of Fortnum and Masons.
Two hundred and fifty coaches transported people to London from cities and towns across the UK, while trains ran at full capacity in expectation of heavy crowds.
The TaxPayers' Alliance set up social media accounts to allow a running criticism of the message from the protest organisers
"Unless something is done to tackle the deficit and growing debt, our children and grandchildren will be paying off our bills for decades to come," said chief executive Matthew Sinclair.
George Osborne admitted during this year's Conservative party conference that further cuts would be necessary to meet his targets. Many financial experts warn another round of spending cuts could smother demand and take damage confidence.