Clashes between demonstrators and police continued into Saturday night as groups set fires and smashed windows. More than 200 people were arrested.
But police said overall, the majority of the protesters, including teachers, nurses, firefighters and students, were peaceful.
Britain faces $130 billion worth of public spending cuts as the government struggles to cut the country's deficit. The government has already raised sales tax, but Britons are bracing for big cuts to public spending.
After the country spent billions bailing out indebted banks, and suffered a squeeze on tax revenue and an increase in welfare bills, Treasury chief George Osborne has staked the coalition government's future on tough economic remedies.
As many as half a million public sector jobs will be lost, about 18 billion ($28.5 billion) axed from welfare payments and the pension age raised to 66 by 2020, earlier than previously planned.