LONDON — Britain’s defense minister, Liam Fox, resigned abruptly Friday after more than a week of damaging newspaper headlines about his personal and professional relationship with a 33-year-old man who accompanied him on numerous official trips abroad and appeared have brokered access for wealthy individuals who shared Fox’s interest in close ties with the United States and Israel.

Prime Minister David Cameron quickly replaced Fox with Philip Hammond, the transportation secretary. Hammond, in turn, was replaced by Justine Greening, formerly a junior Treasury minister.