St. Martin-in-the-Fields located adjacent to Trafalgar Square. This picture was taken from the steps of the National Gallery (which is also, surprise, surprise, adjacent to Trafalgar Square). In addition to the normal religious functions, the church is the venue for many classical music concerts. We attended a Friday evening performance. All of the illumination during the performance was provided by candles set throughout the church. Very cool.

There is a  St. Martin-in-the-Fields web site which includes (among other things) some history and a listing of upcoming concerts.