Last month, the MoD said it had reached an agreement in principle to order the stealth fighters, part of a plan to purchase 14 over the next five years. The aircraft are due to be delivered from mid-2016.

The jets will form part of Britain's first operational squadron of F35s. It has already taken delivery of three training jets, which are based in Florida, and last year ordered a fourth, also for test use.

The contract is part of a wider agreement between the U.S. Defense Department and Lockheed for the production of a total of 43 F-35s for six different countries.

(Reporting by Kylie MacLellan; Editing by Andrew Osborn)