If you follow John [Saunders] Underwood through the censuses, in 1851 he is a road labourer, living in the Toll House, Bedford Street:
https://www.ancestry.co.uk/imageview...79?pId=4270681
In 1861, he is a
carrier (Hooray!)
https://www.ancestry.co.uk/imageview...1?pId=23508196
By 1871 he is an ag lab, using his middle initial:
https://www.ancestry.co.uk/imageview...00?pId=8294609
and in 1881, with a new wife, Fanny, he is a rag and bone dealer:
https://www.ancestry.co.uk/imageview...6?pId=16765110
The chances are that John [Saunders] Underwood had several other occupations over a long working life, but the clues from censuses do, to my mind, confirm that he was Mary Ann's father, but I still had to prove it.
tbc