Although some progress was made in a series of discussions with MOD, significant changes to the offer – for a two-year deal worth 3.5 per cent overall in 2006 – proved impossible because of the constraints placed on the department by the Treasury. MOD is now set to impose the offer in February pay packets.

National secretary Steve Jary said: "Virtually all Prospect members in specialist civilian grades stand to receive just 2.5 per cent. Our members feel that the offer is an insult to loyal, dedicated staff, who have been working hard to maintain and improve support to the front line while facing massive changes in the size and shape of the MOD civil service."

The ballot opens on February 5 and will close on February 19. Prospect represents all specialist staff in MOD including engineers of all disciplines, scientists, logistics support, trainers, librarians, information officers, stores officers and telecommunications staff.