Nearly 100,000 civil servants in three government departments are continuing a 48-hour strike in a row over low pay.
Union leaders claim civil servants are underpaid and undervalued
Picket lines were mounted outside Jobcentres, prisons and Office of National Statistics (ONS) sites as unrest hit the civil service.
Many benefit offices across Britain will stay shut on Wednesday as strike action continues, union officials said.
Public and Commercial Services union (PCS) chief Mark Serwotka said members were "fed up with being undervalued".
The ONS strike, the first to be staged by employees in its history, will last for 24 hours and follows workers' rejection of a 2.9% pay offer.
Action by prison service workers could affect the transfer of prisoners.
The BBC's Labour Affairs correspondent, Stephen Cape, spoke to some of those picketing outside the headquarters of the ONS.
Richard Price, who works at the ONS and is a member of the Public and Commercial Services Union, said the strike is about the "scandalous way the government treats its own employees".
"Around 40% of ONS staff earn less than £15,000 a year," he said.
"We've got problems of absolute low pay and a performance pay system which discriminates in favour of senior managers."
He added: "We've got very low levels of London pay and we've also got the nonsense that you can be 20 years in the same grade and still not be at the maximum of your pay scale."
Mr Price said the problem stretched across the public sector.
"It's high time we had a national pay system as we did over a decade ago," he said.
The Public and Commercial Services Union (PCS) claims many of its members have to survive on "poverty pay".
The biggest walkout has hit the Department for Work and Pensions (DWP) which has been embroiled in an increasingly bitter row over pay which could end up in the courts.
The union says thousands of workers earn less than £10,000 a year and more than 20,000 staff in the DWP have to claim the same benefits they administer, because of their low pay.
The PCS is considering legal action over the imposition of a new pay performance system and has called on government ministers to intervene in the disputes.
The union has warned it will take the department to the High Court unless it withdraws the scheme, complaining that the "unilateral imposition" was a breach of contract.
But the DWP's management have said the pay offer on the table is a "substantial" one - worth an average 5% - targeted towards more junior and less well-paid staff.
Mark Serwotka, the union's general secretary, said: "Members are saying that enough is enough and they are fed up with being underpaid and undervalued."
Some 9,500 DWP workers in Scotland have joined the strike, with an "angry mood" expected at a rally in Glasgow, union leaders said.
Eddie Reilly, secretary for the Scottish branch of the PCS, said benefits payments across Scotland would be affected.
"It's unfortunate that this will impact on the most vulnerable people in society but our members are being paid buttons," he said.
"We cannot rule out further strike action unless they come to the table with a more realistic pay deal."