The Lucas Plan dates back to 1976 and was an effort by workers at arms company Lucas Aerospace to retain jobs by proposing alternative, socially useful applications of the company’s technology and their own skills.

The motion said that in the four decades since the plan was drawn up, Britain’s manufacturing industry has shrunk from 25 per cent to 14 per cent of GDP, with the defence industry now representing 10 per cent of all manufacturing.

Tom Machell (CMD North of England) who moved the motion, met with resistance from Tom James (BAE Surface Ships).

James argued that diversification was a red herring and said the union should focus on defending defence jobs, not looking for other uses for manufacturing skills.

Speaking on behalf of the NEC, Craig Marshall reassured delegates that Prospect would always fight for members’ jobs and that issues like Trident were not up for debate.

Conference passed the motion which instructs the NEC to examine ways of widening the discussion – for example by surveying members or hosting a debate or fringe event on the Lucas Plan at the union’s next conference.