Ed Miliband has told tens of thousands of protesters gathering at the TUC's anti-cuts rally in Hyde Park that they represent "the mainstream majority in this country".
The Labour leader, who gambled against associating himself with potential violence at the 100,000-strong March for the Alternative, said those assembled represented the "big society" David Cameron is so keen to create.
He compared the attempt to derail the government's austerity agenda, motivated by a bid to reduce Britain's structural deficit, with the votes for women, civil rights and anti-Apartheid struggles.
"We are not talking about the politics of envy, we are talking about the politics of fairness," he insisted.
"We do not simply reject the government's policies. We reject the narrowness of their vision, the injustice of their ideology and the poverty of their aspiration for our great country."
Mr Miliband admitted that Labour would have cut the deficit, but insisted it would have done so in a way which protected struggling families and "the promise of Britain" that each generation will do better than the next.
Unemployment was not a price worth paying for tackling the deficit, he claimed, arguing that it would be better addressed by creating jobs.
Mr Miliband suggested the coalition's policies were more likely to divide Britain, dividing north and south, the public and private sectors and those in work against benefit claimants.
"We know, from generations before us, that it is not just politicians who make change happen, it is people," he finished.
"And so when people ask, who will stand up for our NHS? Let us say: we will.
"When people ask who will stand up for our children's centres, let us say: we will.
"When people ask who will stand up for the hopes and dreams of the next generation, let us say: we will."