Complex sentence: All these appointments were unsolicited invitations, the "Monitor" appointment arose because Miller had approached Huw Wheldon about taking up a place on the BBC's director training course, in which Miller was assured that he would "pick it up as he went along".
Split into simpler sentences: All these appointments were unsolicited invitations, the "Monitor" appointment arose because Miller had approached Huw Wheldon about taking up a place on the BBC's director training course. Wheldon assured him that he would "pick it up as he went along".