In act 1 (page11),why does Birling tell the inspector the he was Lord Mayor two years ago and alderman for years?

The inspector asks a direct question: “Mr Croft, when did you first get to know her?” To the horror of Mr. and Mrs. Birling, Gerald confesses that he met her in the music hall in Brumley. He had dropped in after a long day, since the bar at the music hall was “a favorite haunt of women of the town.” He describes Eva as being “very pretty—soft brown hair and big dark eyes.” She was trapped in a corner by Alderman Joe Meggarty, “half-drunk and goggle-eyed,” and Gerald rescued her from that conversation. At the mention of Meggarty’s name, the truth starts spilling out. Mrs. Birling is shocked to hear that Meggarty is “a notorious womanizer as well as ... one of the worst sots and rogues in Brumley.”