A training document, which suggested science teachers engage pupils' attention by getting them to make triggers for bombs, has been withdrawn.

The publication said pupils might like to "use ball-bearings to make tilt switches for bombs".

The document will be withdrawn and we will advise teachers not to use it

Department for Education

But other, "dramatic" official guidance shows pupils how to blow the lid off a tin can by making a bomb of the type used against al-Qaeda cave complexes by US forces in Afghanistan.

The tilt switches idea was one approach in the drive to halt the decline in the number of pupils taking science at A-level and degree level.

The publication containing it, produced by the Centre for British Teachers, was designed to help science teachers inspire pupils in the first year of secondary school.

The document has a foreword by the former education secretary, Estelle Morris, in which she encourages more young people to take an interest in science.

'Not for classroom use'

The Department for Education said it was part of a pack used in a training session for teachers on science teaching.

The department stressed it was not material for classroom use, nor was it designed for pupils.

"The document will be withdrawn and we will advise teachers not to use it," a spokesman said.

"This is not a resource for use in the classroom. We trust teachers' judgement on appropriate teaching in the classroom," he said.

Further bomb-making advice

But another scheme of work for science students involves showing them how to make a thermobaric bomb - one of the most devastating weapons used by the Americans against al-Qaeda cave complexes in Afghanistan.

A thermobaric weapon harnesses the tendency of almost any dust to explode - the cause of many accidents in coal mines and grain stores.

An official scheme of work for teachers of 13 year olds says: "Remind pupils ... that when fuels burn they react with oxygen and release energy.

"Demonstrate this using 2.5cm of icing sugar in a tin-can 'bomb', igniting the fine powder with the flame of a candle and showing that this type of dust explosion can blow off the can lid."

The demonstration seems gratuitous because it is in a section dealing with respiration and the way cells use food molecules after digestion.

"Emphasise that the chemical reaction in cells is much more controlled than the dramatic demonstration," it says.

The Department for Education had no immediate comment.