Thousands of off-duty police officers have taken to the streets of London and tens of thousands of public servants have walked off the job to protest the British government's austerity policies.

Union leaders say more than 400,000 public sector workers went on strike Thursday, while the government said only 100,000 had taken part in what it called a futile effort.

Police are prohibited from striking, but their union said 20,000 officers from across the country, wearing caps with the words “Cuts are Criminal,” marched through London against cost cuts they say will lead to thousands of lost jobs.

Prime Minister David Cameron's government has been under assault since it began slashing spending and reforming pensions to curb the country's debt. But Mr. Cameron's Conservatives and their coalition partner, the Liberal Democrats, have vowed to go ahead with the reforms.

Unions have warned that more strikes against public spending cuts could occur throughout the year, including during the 2012 London Olympic Games, which start in July.