Teaching unions who are set for a day of strike action are standing in the way of "change and reform", the education secretary has warned.

In a speech which sets the government on a collision course with unions, Morris claimed teachers who boycott the government's performance-related pay scheme could jeopardise the progress made since Labour came to power.

Estelle Morris told teachers that they should not undermine her department's plans to deliver reform.

She accused staff of undermining the trust of parents and pupils by returning to the "dark days" of industrial action.

Her speech came as the NUT announced it was going ahead with a one-day strike on March 14 in protest at the new London cost-of-living allowances.

The unions are demanding a significant increase, although ministers have rejected the demand - offering just 3.5 per cent.

Doug McAvoy, NUT general secretary, accused Morris of dealing in spin.

"If this is an attempt by the government to blame others for any adequate investment in education, it will fail. I reject the charge by the government that our day of protest on London allowances is a return to the dark ages," he said.

"Estelle Morris knows that the NUT is working in partnership with her in reducing teacher workload. She must resist the temptation to follow her spin doctors. She must address the problem not shoot the messenger."

The minister, however, pointed to record levels of investment in education - claiming funding per pupil is up £550 in real terms since 1997.

She said improvements had been achieved in reading, mathematical and scientific literacy but warned that this would be put at stake by industrial action.

"The pace of improvement is at risk from a proposed boycott of performance management by the headteachers' associations and the threat of strike action by teachers over the London weighting allowance," she said.

"How can we build the morale of teachers nationally if they are denied rewards for good performance by their own heads?"

"What can I say to parents in London, if their children's education is disrupted by strike action over the London weighting allowance, which last year rose by 30 per cent?

The Tories' education spokesman, Damian Green, said the government's approach was "inept".

"Today's outburst by the secretary of state shows that this government, in its constant search for scapegoats, will pick fights even with teachers who are desperately trying to keep up with the flood of new initiatives, many of which are unnecessary," he said.

"Teachers are not wreckers, they are hard-working professionals who deserve more respect from the government."

Teaching unions reacted with thinly-veiled anger to the minister's comments and announced they had voted in favour of a one-day strike.