Source of the Thames is the last painting on which Andrew's worked and one of his boldest pictures.

In 1992, after fifteen years in Norfolk, the Andrews family returned to London where Andrews took a flat in Albert Bridge Road, Battersea, and set up his studio in Sydney Close, Chelsea. Andrews cycled to the studio each day and began to take an interest in the changing moods of the Thames. He made trips along the river, looked at particular views, executed sketches and took photographs. His fascination with the river Thames was stimulated, in part, by personally felt associations (for instance with Dickens and Turner), but was intensified by the river's deeper metaphorical significance.

In 1994, when Andrews commenced what he saw as an open-ended series of paintings of the river, he was diagnosed with cancer. He postponed his treatment to finish his work on The Estuary. The sequence of execution is as follows: The Thames at Low Tide, Source of the Thames and, finally, The Estuary.

As with all his work, Andrews approached the subject through concentrated research and study, and in keeping with many of his painting - even those exhibited in his lifetime - a question mark remains about whether it was finished. From the earliest days Andrews often combined different handling of the paint within a picture so that different areas have different degrees of finish and often left a painting before it was conventionally finished, so that, for example, areas of drawing and underpainting might remain visible. As Frank Auerbach has written: 'His procedures were such - to me this is amazing - that his paintings were beautiful even when unfinished.' (Frank Auerbach in Michael Andrews. Landscapes, James Hyman Gallery, 2005).

Source of the Thames was characteristically the result of lengthy preparation, began the previous year. The Tate archive contains numerous newspaper cuttings that date from 1993, and include articles on such wide ranging, but still watery, subjects as When did you last see your Father Thames?, Tide of change will bring new life to old Father Thames, Turning the tide of the Thames, Time to pull down Battersea, the centenary of Tower Bridge 1894-1994, The Flood in Florence and Pollution muddles Venetian Waters.

In addition, Andrews collected an array of related material: maps, guides, brochures, angling magazines, postcards and historic photographs. These included a photograph in a newspaper of lugworm diggers, an image of mud flats at low tide in France taken by the U.S. Airforce, William Hogarth's The Shrimp Girl and Victor Prout's photographs from his series The Thames from London to Oxford 1862, namely: No. 16, Marlow from the river, and No. 25, Eton College. (Unpublished material, Tate Archive, Michael Andrews, 2000/25, Box Thames I, II, IV).

The collected material served as inspiration, however indirectly, for his works on the Thames. In addition, he again took his own photographs of the source of the Thames near Lechlade in the Cotswold, the river and beach below Albert Bridge; and other views travelling to the source of the river and walking along its embankment.