More than 18,000 police officers have staged a protest march in London to show their anger at the government's decision not to backdate a pay rise.
The row erupted in December when British Home Secretary Jacqui Smith announced that a 2.5 per cent pay increase, agreed by an independent tribunal, would not be backdated to September as expected.
The government argued that this had been done to keep a lid on public spending. But outraged police officers said the decision effectively cut the rise to 1.9 per cent, less than the rate of inflation and saving the government £30 million.
The Police Federation, a body which represents 140,000 officers in England and Wales, responded by calling for Ms Smith to resign and saying it would ballot its members on whether to overturn a ban on strike action.
The protesting officers began their march at Hyde Park at about 11.30am, stopping off at the Home Office to deliver petitions from every force in England and Wales, and finishing at the Tate Gallery.
Rallies were then due be held in Westminster.
Those taking part have been instructed to behave in a dignified and controlled manner amid suggestions that groups with grudges against the police might try to stage rival protests.
Since the dispute began, British Prime Minister Gordon Brown has insisted that the government would not back down, saying the pay increase was in line with other public sector deals and had been made in the national interest.