On behalf of 15,000 scientists, engineers and managers, Mike Clancy, national secretary of Prospect, said: "The government may try to focus on the cash out-turn. But the reality is that our members will be asked to do more and more with less and less resource.

"MOD has committed to find £2.8 billion of savings and cuts of 10,000 civilian jobs but it does not have a clue how to achieve them. It has set in motion a string of reviews but their outcome is far from certain even if the Defence Secretary pretends they are in the bag.

"We challenge Geoff Hoon to prove that both the work and the manpower targets he has set are not arbitrary targets."

Prospect stressed that MOD must maintain a balance between public and private sector delivery. "It is a false economy to transfer work out of MOD but then still have to employ private contractors at greater expense to get the job done," said Clancy.

He warned that the extent of the Defence Change Programme, which includes sweeping changes to human resource procedures across the department, was creating "a demoralised and demotivated workforce" which would not be able to perform the tasks asked of it.

The union will challenge any move to impose compulsory redundancies. MOD is still fighting to overcome recruitment and retention problems in key areas of the department, such as a shortage of procurement skills in the Defence Logistics Organisation, said Clancy.