The NUT will campaign for pupils to hear from speakers “promoting alternative points of view” and to have “education for peace embedded in the curriculum”. Stefan Simms, a delegate from Ealing, west London, said young troops were being used as “cannon fodder for the profits of oil companies.

“I would be personally gutted after years of putting time and professional effort into the students I teach, helping their education and preparing them for adult life, to find out that some of them have said ‘I decided to join the Army’.”

The MoD hit back at the delegates’ vote, denying that it actively ran recruitment campaigns in schools.

Brigadier Andrew Jackson, Commander of the Army Recruiting Group, said: “The single-Service schools teams visit about 1,000 schools a year, only at the invitation of the school.

“Their aim is to raise the general awareness of the armed forces in society, not to recruit.

 “We are proud of the work we do with schools and colleges to inform young people about the tremendous work and careers on offer, which can provide fantastic and unique opportunities to a wide range of people from all sectors of society.”

An MoD spokesman said: “Our recruitment practices avoid ‘glamourising war’ and ‘propaganda’.

“Anyone considering a career in the armed forces is presented with clear information and all aspects of service life are discussed in detail, following a sensitive recruitment process.

“A career in the armed forces provides amazing and unique opportunities. Armed forces careers must compete against other potential employers.

“It is fair that they have the opportunity to recruit people when they are legally able to leave school.

“The recruiting process is designed to protect the interests of the applicants at every stage, regardless of age.”