This is the third episode of this intense, searingly acted semi-autobiographical story by Edward St Aubyn, who used his Patrick Melrose novels and alter ego to exorcise some very traumatic childhood memories and demons. Benedict Cumberbatch stars in the title role – and, in flashbacks, Hugo Weaving and Jennifer Jason Leigh are riveting, and sometimes revolting, as young Patrick’s well-to-do, but seldom doing well, parents.