The biggest strikes for many years are affecting Britain, as public-sector workers protest against proposed cuts to their pensions.
Unions say 750,000 civil servants - a fifth of all public-sector employees - stopped work and several thousand people marched through the central London on Thursday.
They walked to Westminster where the leaders of the four unions involved attacked the coalition government and Labour leader Ed Milliband, who has described the strikes as a mistake, the BBC reports.
The Public and Commercial Services union told the rally that 85% of its members had walked out on Thursday, disrupting courts, ports, airports, museums and government departments.
The union warned it would strike again if necessary and other unions were likely to join.
Teachers from three unions walked out, with at least 40% of state schools in England and Wales disrupted.
Workers in many government departments and agencies also did not turn up for work, and their union said turnout was strong throughout Britain.
The government has condemned the action, saying the public sector pension plans are "fair to taxpayers" and the other 25 public sector unions not on strike on Thursday were continuing with negotiations.
The Public and Commercial Services union said early indications from pickets suggested about 210,000 of its members participated in the strike.
However, the government said figures gathered "from every government department" indicated that just under 100,000 civil servants went on strike, meaning 75% were at work.