Sherlock has got consistently high ratings, much higher than you'd expect on British TV, even in a primetime, 9pm slot. So while The Blind Banker only brought in an audience 8.07 million, that really stands as how popular the show is; this year Doctor Who only passed that once (with the series premiere, Deep Breath). The second episode of the first series, The Blind Banker's drop-off can probably be chalked up to people not realising how much of a phenomenon the show would be at that point. The fact that the show has always been getting such consistently high ratings says a lot about both its quality and the devotion and breadth of the fan-base; the later two episodes of Series 3 got exactly the same audience numbers, indicating once people are hooked, they're properly hooked.