The FTSE 250-listed engineer added that the amendment is to a 25-year contract under which it provides experimentation, test, evaluation and training support to the MoD.
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It said the contract generates revenue of around £220mln a year for delivering core capabilities such as the operation of sites and a further £100mln a year for project tasks such as conducting trials.
Under the amended agreement, the group will modernise 16 critical defence facilities in the UK, with the ministry to invest £190mln in modernising the infrastructure, equipment, and working practices across all the sites.
QinetiQ said it will fund the capital investment and will subsequently recover it from the MoD over the life of the contract.
Steve Wadey, QinetiQ’s chief executive, commented: "Today's agreement enhances our contribution to the safety and operational effectiveness of UK armed forces in an era when threats to our security remain acute and are changing rapidly. In line with our strategy, we are introducing innovative ways of working and making selective investments to reinforce the UK's position as a world-leader in the generation and assurance of military capability.”
In afternoon trading, QinetiQ shares were 1.7% higher at 306.40p.