Thank you for your assistance and interest.
Latest developments:
John William Banks (1787-1868) has died at 1 Meilor Place St. Olave and his wife Sarah Elizabeth Banks died 26 Dec 1882 15 Idonia Street, which I think in Greenwich, the home of her daughter.
The birth of a son Charles Banks in 1840 was the only record now sourced, to indicate that his mother was Sarah Elizabeth Franks, b. 1801 the daughter of John and Hannah Franks of Surrey.
We have not located a marriage and they had a son John William Banks born 21 Feb 1821 St. Olave.
There is a marriage of a John Banks to Sarah Banks 17 Nov 1822 St. George Bloomsbury
and there is a marriage of a John Banks to a Sarah Franks but not until 11 Apr 1836 St. Leonard's Shoreditch.
As John Banks was 33 in 1820, it remains possible that John Banks was separated from a previous marriage and took Sarah Franks as his partner in 1820, then officially married her in 1836.
Thus, any helpers may offer to help search for a marriage in 1820/1821 for a John Banks to a Sarah Elizabeth Franks.
Keith