Also known as the London Oratory and the Oratory of St Philip Neri, this Roman Catholic church is second in size only to the incomplete Westminster Cathedral. Built in Italian baroque style in 1884, the impressive interior is swathed in marble and statuary; much of the decorative work predates the church and was imported from Italian churches. Intriguingly, the church was employed by the KGB during the Cold War as a dead-letter box.

There is a busy schedule of services (five on weekdays, more at the weekend), including a Solemn Mass in Latin on Sundays (11am).