The call comes after confirmation that the privatised defence agency is set for a £1.1bn initial public offering.

On behalf of 3,000 members in QinetiQ, Prospect National Secretary David Luxton said: "Whilst today’s announcement has ended months of uncertainty, senior managers are going to have to explain to staff why such large returns have been confined to so few.

"The disparity in the distribution of shares amongst employees (which was decided by the Carlyle Group) is a lost opportunity to reward all QinetiQ staff who have contributed to the success of the company. Most QinetiQ staff were not given the opportunity to purchase the highly geared share options available to senior management that will now generate a massive windfall on flotation."

QinetiQ was formed from the majority of the MOD’s Defence Evaluation Research Agency (DERA) in 2001 and effectively privatised the following year. At present the company is jointly owned by MOD, which owns 56%, and the Carlyle Group, which purchased a 31% stake in 2002.

Although the remaining 13% of shares were allocated for employees, over three-quarters of staff are unlikely to benefit from the windfall, even though they provide the intellectual assets that have made QinetiQ so successful.

MOD and the Carlyle Group are set to see large returns on their money following the stock market launch. In addition, senior managers have had privileged access to share schemes which could generate millions of pounds on their behalf.

QinetiQ employs over 8,500 staff in Britain and in North America where it has recently acquired new businesses.