From the Wikipedia page 
Holy Trinity Church Marylebone, Westminster, London is a former Anglican church, built in 1828 by Sir John Soane. In 1818 parliament passed an act setting aside one million pounds to celebrate the defeat of Napoleon. This is one of the so-called "Waterloo churches" that were built with the money. It has an external pulpit facing onto Marylebone Road, and an entrance with four large Ionic columns. There is a lantern steeple, similar to St Pancras New Church, which is also on Euston Road to the east.
By the 1930s, it had fallen into disuse and in 1936 was used by the newly-founded Penguin Books company to store books. A children's slide was used to deliver books from the street into the large crypt. In 1937 they moved out to Harmondsworth, and SPCK moved in. It was their headquarters until 2006, when they relocated to Tufton Street, Westminster (they have since moved again to Pimlico); the church is now used as offices. In 2009 an art exhibition was held there, the centrepiece of which was a crucified ape. There are currently proposals to turn it into a shopping arcade. It stands on a traffic island to itself, bounded by Marylebone Road at the front, and Albany Street and Osnaburgh Street on either side; the street at the rear has no name.