The National Union of Teachers has put itself on a collision course with ministers with a warning that schools are facing a looming cash crisis.

Following a clash with the government over plans for classroom assistants, the union was using the first day of its annual conference to warn that pupils will suffer unless more money is found.

Teaching leaders say that additional cash settlements have failed to cover increased spending on staff costs and pensions contributions.

As a result the union is warning that teachers may be laid off and classrooms forced to close.

NUT chief Doug McAvoy said: "Pressure on school funding is causing threats of reducing the number of teachers and even teacher and support staff redundancies.

"It is even more important that changes to the contract and to the regulations are protective of teachers and teaching."

The union is also set to debate strike action over the government's plans to introduce classroom assistants.

The NUT has warned it will boycott any moves which result in untrained staff teaching in the classroom without a qualified teacher present.

Relations between the union and ministers have reached an all time low and appear set to worsen over coming weeks.

Charles Clarke announced earlier this year that we would break with tradition by rejecting an invitation to address this weekend's conference.

For the first time in the union's history, no government minister will address the annual gathering.