The UK’s first Lockheed Martin-built F-35 Lightining II production aircraft has flown its inaugural flight from Lockheed Martin’s Fort Worth facility in Texas, US.

The short takeoff/vertical landing (STOVL) variant jet, BK-1, made a series of functional flight checks during a 45-minute sortie on Friday April 13, 2012.

Prior to acceptance from the UK Ministry of Defence, the jet is to complete a series of company and government checkout flights, after which the jet will be used for training and operational tests from Eglin Air Force Base in Florida, US.

Joint Strike Fighter UK National deputy group captain Harv Smyth said, "Not only is this a watershed moment for the Joint Striker Fighter program, since BK-1 is the first international F-35 to fly, but it also brings us one step closer to delivery of this essential 5th Generational capability for the UK."

BK-1 is the first of just three F-35 fighters that the UK has committed to buying, as the final size of the nation’s F-35 fleet has yet to be decided owing to budget restraints enforced by 2010’s Strategic Defence and Security Review.

Whereas the UK had originally opted for the F-35C variant, speculation has continued to mount that the MOD could revert to the F-35B variant in order to save money.

The F-35C variant would require the installation of catapults and arrestor wires on the Queen Elizabeth class carriers that are planned to host the fighters, costing up to £1.8bn per ship.