John McCain faced fresh scrutiny of his role in the award of a $35bn (£17bn) Pentagon contract to EADS yesterday after it emerged that some of his top advisers lobbied for the European aerospace group to win the deal.

Mr McCain, the presumptive Republican presidential nominee, has portrayed himself as a neutral watchdog in the long battle between EADS and Boeing to supply a new generation of refuelling tanker aircraft to the US air force. But the revelation that three of his aides lobbied for EADS threatened to deepen the perception that Mr McCain helped steer one of the biggest military procurement contracts in recent years into foreign hands.