Ronald Sugar, chief executive of Northrop Grumman, which is vying with Boeing over a $35bn US Air Force tanker contract, has warned of “dire consequences to the transatlantic alliance” should the competition be influenced by protectionism.

The tussle between Northrop and European partner EADS, and Boeing for the contract to provide refuelling tankers to the USAF has attracted an unprecedented amount of political attention in recent months. Northrop and EADS originally won the contract in February, a victory some Boeing supporters warned would cost American jobs.