Trade union leaders warned that yesterday's strike by teachers and civil servants would be followed by an "autumn of discontent" across the public sector unless the Government retreats over plans to cut their pensions.
The unions also turned their fire on Ed Miliband after he criticised the 24-hour strike which disrupted more than 11,000 schools and forced many parents to make emergency childcare arrangements.
Mary Bousted, general secretary of the Association of Teachers and Lecturers (ATL), won the biggest cheer at a Westminster rally when she said: "The response of Ed Miliband has been a disgrace - he should be ashamed. If our strike is a mistake, what has he done to oppose this devastating attack on our pensions? If the Opposition will not defend our pensions, we will."
Protests were staged in about 80 towns and cities. After a march by 20,000 protesters in London, 37 people were arrested for offences including possession of drugs, criminal damage, breach of the peace and an alleged breach of a by-law at Trafalgar Square. One police officer and six members of the public were injured but Scotland Yard said scenes had been "largely peaceful".
Downing Street said essential services were maintained, with only a "minimal impact" on services such as courts, 999 calls, passport controls and job centres.
The Government said 105,890 civil servants walked out, meaning that 80% of the Civil Service worked normally.
The Public and Commercial Services Union (PCS) insisted the figure was double that in its biggest-ever strike.
The Department of Education said 11,114 of the 21,500 state schools in England were affected, with 5,679 shut and another 4,999 partially closed. Some 201 academies and city technology colleges were also shut, while 235 remained partially open.
Both the ATL and the National Union of Teachers said the figure was a lot higher, with 85% of schools disrupted.
Mark Serwotka, the PCS general secretary, warned that the ranks of the strikers would grow to four million by the autumn unless ministers backed down. He said the action would be "much much bigger and will involve more unions". what now?
The Treasury wants a deal with unions by November so that higher contribution rates, smaller pensions and a later retirement date can start to be introduced from next April. Hardline unions plan to build up the pressure during the TUC and Labour conferences in September and the Conservative conference the following month.