If we are talking about the power of TripAdvisor, we should take into consideration Top Attractions in England (Travelers' choice in 2014):
1. National Gallery (London)
2. British Museum (London)
3. Victoria and Albert Museum (London).
As you see, all attractions are located in London. And quantity of reviews is over 10k. The other places are not so popular (less 1k of visitors' reviews). But also they are beautiful and worthy to visit outside London.