Demonstrators gather in central London as they prepare to march against the government's austerity policies and call for an alternative economic strategy that puts jobs and growth first.
Government spending cuts brought some tens of thousands of people on to the streets of London and other British cities on Saturday in protest, with union leaders expected to call for a general strike.
Marchers carried signs reading "No cuts" and "Tax justice not tax havens", condemning the austerity measures introduced by Prime Minister David Cameron's coalition government in a bid to reduce Britain's huge deficit.
"Austerity isn't working. It is hitting our jobs, our services, our living standards," Brendan Barber, general secretary of the Trades Union Congress (TUC) umbrella body, told a rally at the end of the march in Hyde Park.
"Ministers told us that if we only accept the pain, recovery would come. Instead we have been mired in a double dip recession."
Britain climbed out of a deep economic downturn in late 2009 but fell back into recession at the end of 2011.
Opposition Labour leader Ed Miliband was also due to speak at the Hyde Park rally.
Protests were also being held in the Northern Irish capital Belfast and the Scottish city of Glasgow.
Dave Prentis, leader of Britain's biggest public sector trade union Unison, said government cuts were pushing hundreds of thousands of state employees out of work.
"We are here for the millions of people who don't have a voice," he said. "We just can't take any more."
But Cameron, whose Conservative Party shares power with the centrist Liberal Democrats, insisted that the measures were needed to balance Britain's budget.
"Today Ed Miliband is headlining a rally calling for an end to every single spending cut needed to clear the deficit," he said in a message posted on his Twitter account.
Miliband was expected to tell the Hyde Park rally that whoever was in government would have to make some cuts, while adding, "I do not promise easy times, but I do promise a different and fairer approach."
London's Metropolitan Police did not provide an estimate for the number of demonstrators, but the TUC said it was expecting tens of thousands of people to join the 4.8-kilometre march. – AFP.