Turning on his coalition colleagues, the senior Liberal Democrat said he opposed attempts to tighten the law around industrial action. Trade unions should not need to get approval for a strike from half their members when MPs do not need to reach such a high threshold to get elected, he said.
"We disagree with the Tories' assertion that a small turnout in strike-action ballots undermines the basic legitimacy of the strike," he said. "If they want to look at minimum turnout, this would have major implications for other democratic turnouts and elections. Many MPs have been elected by well under 50% of their electorate, let alone police commissioners or MEPs. Why have a threshold in a ballot but not make our elected politicians or shareholders face the same hurdle?"
Hundreds of thousands of public sector workers, including teachers, firefighters, care workers, refuse collectors, librarians and other civil servants went on strike in what the unions described as the biggest round of industrial action for three years.
Unions have claimed up to a million stayed away from work but the Cabinet Office estimated the figure at about 500,000. The government said all job centres were open, four out of five driving tests went ahead as planned and the majority of schools were open in England and Wales.
The Conservatives have been increasing their attacks on the trade unions over recent days ahead of the strikes. They are currently looking at putting a time limit on the validity of strike ballots and forcing trade unions to win support from a minimum number of members.
David Cameron's official spokesman said any disruption of public services is always wrong.
"Does the prime minister think that people in this country – parents, commuters, users of public services – should have their routines disrupted? Of course he doesn't think it is right. He would say that if you are an individual affected by disruption, the disruption will be significant – for example if it is your school that is closed. That is why any disruption to any user of public services is wrong."
In an interview for the House magazine, Francis Maude, minister for the Cabinet Office, even suggested allowing parents and governors to break the teachers' strike by coming in as volunteers.
"I know the Department for Education is thinking very carefully about what can be done to enable volunteers to come in, for example governors who will all be vetted and have clearance, could go in and act as volunteers to supervise and just to enable the school to stay open, given that this is NUT absolutely out on its own, none of the other teachers' unions are doing this," he said.
"So I think there will be a real effort to keep schools open because the damage is very substantial."
Labour hit back at the Conservative efforts to tighten the laws around strikes, saying millionaire cabinet ministers should stop demonising some of the UK's lowest paid workers who are on strike over their wages and conditions.
Michael Dugher, Labour's shadow Cabinet Office minister, said it was "pathetic" that the government was acting with belligerence towards those taking industrial action, rather than trying to negotiate. The government should bear much of the blame for the situation because of its decision to "ramp up rhetoric", he said.
Labour said it did not support the strike but would not condemn those who were protesting against low pay and changes to their conditions.
Dugher told the House of Commons: "We have said on these benches repeatedly that no one wants to see strikes, not least because of the impact they have on children, on parents, on all of those who rely on vital local public services. Strikes represent a failure on all sides and all sides have a responsibility to prevent strikes from taking place."
He said it was an "unedifying spectacle" to see ministers rowing in public with the civil service.
"We have had yet another depressing demonstration of a cabinet full of millionaires demonising the lowest paid in society," he said.
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