You're welcome. It was pure luck finding that 1861 census when I searched using Devizes as a keyword, it was lucky that he used that as a place of birth on one census.
It looks as if the family moved to London at some time between the marriage and the birth of the first son, and then returned to Devizes before the death of Thomas in the March quarter of 1854. His son was born just after his death, in the June quarter of 1854. Perhaps Thomas was ill and returned home to die and so that his wife would be near family. A similar thing happened in my family. My gx2 grandfather and family moved to London from Suffolk and my great grandmother was born there. Then the next thing I found, three months later, was his death from TB back in Suffolk, and the family there in the following census.
Perhaps your William was aware that he was born somewhere in London, but because he lived in Devizes as a young child, probably also considered that is where he came from.
