United only has pilot bases in the US. It is possible that some commute from overseas. But they only fly one type of aircraft at a time. So he can't fly the 777, then the next trip fly a 767. Those are different type ratings. (757/767 the same type rating though) So if he says he's based in the UK and on one trip flies the 777 and then the 767 on another, he's not a pilot.