By Rory Maclean, James Westhead and Sean Coughlan BBC News Online at the NUT conference

Ministers seem set to make a significant concession over reducing teachers' workload in England and Wales - with the offer of guaranteed lesson preparation time in the school day.

As the National Union of Teachers threatened industrial action in a campaign for a shorter working week, BBC correspondents have found that teachers could be about to receive an improvement in working conditions.

There seems likely to be an offer of up to five hours a week of "professional time" which would allow planning and marking within the school day, rather than in their own time.

The Department for Education and Skills, likely to be embarrassed by the timing of such a leak, described the claims as "pure speculation".

Education Secretary Estelle Morris has emphasised that she will not respond to threats of strikes - and the government will not want to appear to be making concessions only hours after teachers voted for industrial action.

Teachers have complained angrily about a culture of excessive working hours, which they say causes stress and damages recruitment to the profession.

And the union's general secretary, Doug McAvoy, had earlier said that such an offer of five hours preparation time would represent a "very significant development".

38-hour week?

The biggest teachers' union has also indicated that a breakthrough was possible - and has made clear its readiness to compromise.

The demand for a 35-hour working week for teachers is open to negotiation, says Mr McAvoy.

He indicated that if the government suggested a 38-hour working week it would be accepted by the teachers' union.

At present, the Education Secretary, Estelle Morris, is refusing to accept any fixed limit on working hours.

But Mr McAvoy expressed confidence that ongoing negotiations with government would resolve their differences - and he made clear that the much-quoted claim for a 35-hour week was not cast in stone.

Although he suggested a 38-hour system as an "illustration" of how a working week might be developed, he also indicated that a higher figure would not necessarily be rejected.

Cutting a deal

According to an official independent review, teachers are currently working an average of 53 hours a week.

And Estelle Morris, speaking to journalists at the conference on Saturday, suggested that non-teaching tasks accounted for 20% of a teacher's working week.

She proposed that such tasks could be carried out by classroom assistants.

This would reduce the teachers' working week to around 42 hours - only four hours above the 38 hours being floated by Mr McAvoy.

If the five hours of "professional time" were added to this, a deal could be closer than is apparent from the threats of industrial action.