Schools and politicians are facing a new era of teacher union militancy, the NUT and the NASUWT conferences heard last weekend.

Meeting in Liverpool, the NUT voted to ballot members on strike action over teacher workload while in Birmingham the NASUWT vowed to take action over a threat to pensions and plans to “break up state education”.

NASUWT general secretary Chris Keates said schools had enjoyed one of the calmest periods in industrial relations for 30 years, but that “at some point you have to draw a line in the sand”. The union strongly opposes Conservative plans to allow parents and not-for-profit charities to set up “free schools” removed from local government accountability.

On Monday, for example, the NUT conference reverberated with chants of “workers united will never be defeated” as a union leader described the Government’s behaviour as an employer as “the worst in the history of the country”.

Delegates gave Mark Serwotka, head of the Public and Commercial Services Union, a standing ovation for his blistering attack on Labour’s track record.

He called on unions to “stand together” and take industrial action if necessary to defend jobs, pay and pensions.

He said: “In the civil service, the people I’m representing, in four years, the last four years of New Labour, we’ve lost 100,000 jobs, 2,000 offices have closed.

But he added that he was under “no illusions” that Tory leader David Cameron would be a better prime minister than Gordon Brown.

“He’s going to be dreadful,” he said.

And the NUT voted overwhelmingly to take action over what it argues is excessive workload, calling for teachers to have the right to a 35-hour working week.

Ms Keates attacked the Conservatives’ plans for “free schools” and its promises to give teachers greater autonomy.

She said the union would not fight the plans single-handedly, but try to mobilise support from parents and the local community, a tactic that had succeeded in its disputes with some academies.

“It’s freedom, in our view, to reduce the vision for 21st century schools to children being educated in a run-down flat over an off-licence. It’s a corrupted definition of what freedom means - schools will be free to do what they choose as long as it’s OK with you.

“Please stop the pretence that schools will be free or teachers will be free under a Conservative government.”

Ms Keates said the overwhelming public opposition to free schools, shown in a recent Ipsos Mori poll, left “the Conservative education policies in tatters”.

NASUWT delegates also vowed to “go into battle” if the new Government creates a “death sentence” by raising the retirement age and introducing new taxes on pensions.

Members said they will press for industrial action if they are forced to work until they “drop” because of the economic crisis.

Shadow chancellor George Osborne wants to cut the cost of public sector pensions, which could balloon by 200 per cent to pound;79 billion a year by 2060. The NASUWT claims the Tories will tax pension lump sums and make people work after the age of 65.

NASUWT delegates unanimously voted to “defend” their pension and start organising their “battle”.

“If David Cameron presses ahead with ideas to tax teachers’ pensions as a quick win to bring in revenue it will be the biggest mistake of his political life,” said executive member Dave Wilkinson.

“If they do that we will go into battle, we will press for industrial action and we will win. Today we are drawing our line in the sand.”

Meanwhile in Liverpool, the NUT agreed to a national ballot of members over “strike and non-strike action” if a new national contract limiting working hours and excessive workload cannot be agreed with ministers.

The union has also promised to hold ballots for action to support members who are victims of bullying by headteachers or face harassment because of their union work.

Calling for a 35-hour working week, Martin Powell-Davies, a member from Lewisham, south London, told the NUT conference in Liverpool: “We need to prepare for a national ballot for strike action, bringing all our members together. We’re going to warn the new government that we are ready to act.”

Sue McMahon, from Calderdale, West Yorkshire, told the conference that the widely expected cuts to education funding post-election would result in axing line-management positions, with responsibilities falling on classroom teachers.

She also blamed the Government’s obsession with data for leading teachers to do more unpaid overtime than ever.

“Our schools are sinking in a pernicious bog of foul-smelling data that we as professionals are expected to focus on,” she said. “Our workload has increased but our professionalism has been eroded.”

Ken Rustidge, an executive member, said that the 2003 Workload Agreement had “utterly failed” and that 10 per cent preparation and planning time is “woefully inadequate”.

Others warned that the extra workload on teachers was often dressed up as “CPD” or career development opportunities.

In one of its stranger moves, the NUT called for the nationalisation of any private-sector firm that threatens major job cuts.