The Custom House is on the right, with the Monument behind it and to its left the church of St Magnus the Martyr and the dome of St Paul’s Cathedral. The Pool is busy with craft. Although sketched quickly in outline, the composition is the same as in Turner’s watercolour The Custom House (Vancouver Art Gallery)1 engraved by J.C. Allen, 1827. See Introduction to the sketchbook for plans for a series of London subjects in the 1820s. Other more developed drawings of the Custom House in the book, for example folio 75 verso (D07083; Turner Bequest CV 66a), show the central façade added by Robert Smirke in 1825 to the earlier building by David Laing. Generally, these adopt the same viewpoint and must be connected with the same project and contemporary in date.
Andrew Wilton, The Life and Work of J.M.W. Turner, Fribourg 1979, pp.358–9 no.516.